Beyond the Human Eye

Better than Cannabis.....

2012-01-11T17:51:00.000Z

There was a time – before the advent of synthetic fibresbased on plastics and petrochemicals - when the wealth and security of nations depended on tough, coarse plant fibres that provided rigging for sailing shipsand the raw material for countless other essential objects - like sacks and sails for example - soexplorers were always on the look-out for new supplies of this strategicmaterial.

Joseph Banks,travelling on Captain Cook’s first voyage to the South Seas in 1769, had highhopes that he might make a fortune from growing New Zealand flax Phormium tenaxthat he found in those Antipodean islands, as a substitute for cannabis fibre which, up until then, had provided most of the fibre for rigging naval vessels. Maorismade their traditional textiles from the Phormium fibres but Banks envisaged a thriving industrial market for the product, whose fibres are much stronger than those of cannabis, and an attempt was made to use convicts to grow the plant as a fibre crop on Norfolk Island. Banks was destined to be disappointed - you can read an account here - but it did become an important source of fibre for rigging in the 19th. century..

The image above shows a transverse section of a New Zealand flax leaf, using the fluorescent dye auramine O to stain the lignified fibres, which show up as the transverse yellow-green bands in the image. I've turned the natural orientation of the leaf 90 degrees clockwise, to fit the page.

The thick-walled fibres have a tiny central cavity (the lumen), which is typical of sclerenchymatous fibres.

The transverse red bands are photosynthetic parenchymatous cells - chlorophyll fluoresces red in the blue light that was used to illuminate the specimen.

The bright blue cells are bundles of thin-walled phloem, which has no lignin in its walls, and the brighter yellow cells surrounding the phloem will be lignified xylem, conducting water.

The lower surface of the leaf, to the left of the image, has a lignified hypodermis, below the epidermis.

The natural function of the fibres and lignified hypodermis is to provide structural rigidity for the long, narrow, sword-shaped leaves, which are held upright in the living plant, which is illustrated below (public domain image from Wikipedia Commons http://upload.wikimedia.org/wikipedia/commons/a/a5/NZflaxPiha02.jpg

Today Phormium tenax is mostly grown as a decorative garden plant.

Micro-rock-pooling in Winter.

2011-12-30T15:32:00.000Z

It's too cold in winter to spend a lot of time paddling around in rock pools but you can always take a few samples of seaweed home on a jar of seawater and have a look at the smaller inhabitants under the microscope. These two, each about a millimetre long, were in a sample of Corallina officinalis seaweed. The upper specimen is an unusually bristly acarine mite, found clambering through the seaweed fronds. You can see more acarine mites by clicking here.

This is a minute flatworm, with two very simple eyes, found gliding over the surface of the seaweed, propelled by thousands of cilia that are only visible at high magnification under the microscope. You can see another marine flatworm, in more detail and with a movie of the cilia in action, by clicking here.

Sowing Wild Oats

2011-12-23T20:34:00.000Z

Some seeds need to be sown while others - like wild oat Avena fatua - sow themselves. This is a wild oat fruit (or, to be botanically accurate a caryopsis) in the dry state. It's equipped with a long awn (which is extension of the floret in which the fruit formed and in which it is shed), that's bent at a right angle about a quarter of the way along it's length.

When the caryopsis falls to the ground and gets wet - from a passing shower of rain, for example, that bent awn straightens, then bends again as it dries out. The picture above shows the same fruit, but now it's been moistened and the awn has straightened. As the awn bends and straightens it also rotates, because the awn is constructed from a helix of fibres that twist and generate torsion as they dry (see below).

The outer coat of the floret containing the caryopsis is equipped with this arrowhead of stiff hairs at the tip ....

.....which readily catch in fur and feathers and help disperse the seed, but also anchor it in crevices in the soil when it falls to earth.

There is also a beard of stiff hairs running up the groove in the caryopsis. As the awn rotates .....

.... with the expansion and contraction of this helical tube of spiral fibres that it's constructed from, it levers the caryopsis further into soil crevices. Those stiff hairs on the caryopsis help to anchor it in the soil, ratcheting it in ever deeper until it's in a moist enough position to germinate and put down roots.

This is a seed that sows itself.

The video below shows a group of wild oat caryopses writhing as their awns dry out and begin to rotate.

Breathing Space

2011-11-27T09:03:00.001Z

This is a thin section of the lower stem of water milfoil Myriophyllum sp. , stained with the fluorochrome calcofluor which binds to the cellulose of the cell walls and is fluorescing brightly in ultraviolet light. Marsh plants tend to be rooted in anaerobic mud and so have air channels (aerenchyma) that conduct oxygen down to the roots.

Working from the outside inwards in this section, there is a well defined single outer layer of very small cells forming the epidermis, then inside that lies the stem cortex with 17 air channels arranged around the central stele, which contains the phloem (brightest flourescence) and the xylem.

The stem and leaves of water milfoil. The small white structures in the leaf axils are the stigmas of the female flowers.

Plant Cuticles

2011-11-10T14:42:00.000Z

The surface of plants (with a few exceptions, such as those that live submerged under water) is covered with a tough, transparent, waxy layer called the cuticle, composed of cutin secreted by the layer of epidermal cells that it covers. The best way to see the cuticle is to snap the leaf of a drought-adapted succulent plant like Crassula ovata and pull one part of the leaf against the other, peeling away the cuticle, which covers the above ground parts like a wrapping of cling-film.

These cuticular peels, often with a single layer of epidermal cells attached, can be mounted on a microscope slide .....

..... and viewed to reveal the pattern of cells and the .....

...... stomata, which allow carbon dioxide to enter for photosynthesis. The two images above are of cuticular peels of spiderwort Tradescantia virginiana.

In this vertical section of a leaf, stained with fluorescent dyes, the cuticle appears as the bright yellow layer on top of the epidermal cells. In the centre you can see a single stoma in vertical section, with closed guard cells and its adjacent subsidiary cells, with a sub-stomatal cavity below leading to the loosely packed mesophyll cells, where photosynthesis takes place. The cuticle has a dual function - keeping water in and keeping the leaf surface dry.

In plants adapted to arid conditions (xerophytes), like this Aloe variegata , the cuticle is visible as an extremely thick transparent layer that allows very little water to escape from the leaf.

In plants that are subjected to frequent rainfall, like this nasturtium Tropaeolum majus leaf, fine grooves in the cuticle surface trap air below the water droplets, which then round-up under their own surface tension and simply roll off the leaf when it shakes in the wind. This is vital, as a wet leaf surface blocks stomata and prevents carbon dioxide from entering, slowing down photosynthesis. As the water rolls off the leaf it carries away dirt and dust, so the leaf cuticle is effectively a self-cleaning surface - a phenomenon known as the 'lotus effect', referring to the extremely hydrophobic self-cleaning leaves of sacred lotus. The silvery area under the central water droplet in the image above is caused by minute air bubbles, trapped between the water and the leaf surface.

The cuticle can also have a secondary defensive role, as seen in this painfully prickly leaf of the hedgehog holly Ilex aquifolium 'ferox', which is covered in cuticular spines. In general, leaves of evergreens, that survive for several years before they are shed, tend to have thick cuticles that protect the leaf against herbivore attack throughout their extended life.

Springtails

2011-11-03T12:11:00.000Z

Every time I lift the lid of our garden compost bin scores of these tiny insects, each smaller than the diameter of the head of a pin, leap around in all directions. They are members of the ancient insect order known as the Collembola - commonly called springtails - and feed on decaying vegetation. The darkness, warmth and humidity of the compost bin suits them perfectly. I think this species might be Folsomia candida, which is very common in gardens.

Most of the time they move slowly on those stumpy legs but when they are alarmed they hurl themselves into the air using an organ called a furcula under their tail .....

.... which you can see in this specimen. You could liken its action to a kind of exceptionally energetic pole-vaulting. The tip of the furcula is held in place by a clip-like structure called a retinaculum, but when the muscles in the furcula contract the clip suddenly releases its grip and the furcula flicks downwards and backwards, hurling the animal upwards and forwards.

You can find pictures of another springtail species here and a fine set of photographs for ID purposes here.

Was Sid, the Mystery Microscopist, a Scotsman?

2011-10-31T11:19:00.000Z

When I was exploring the old microscope slides belonging to the mysterious 'Sid' that I mentioned in my previous post I came across one that was clearly home-made and was labelled as porphyritic olivine basalt from the Lion's Haunch, Arthur's Seat, Edinburgh. The hill is the plug from the mouth of a long extinct volcano, exposed after softer sedimentary rocks were eroded from around the igneous core. Polarised light microscopy reveals the crystalline inclusions very nicely.

Similar rock samples were collected on the Apollo 15 mission to the moon in 1971

Arthur's Seat is the very conspicuous hill - some might call it a mountain - almost in the centre of Edinburgh. From the right angle it looks like a resting lion and this polished thin section of igneous rock came from the 'Lion's Haunch'. Of couse, there's no way of telling whether Sid, who was apparently a chemist, prepared this specimen himself or swapped it with a geologist friend - microscope slide exchange clubs were once common - but he clearly had an interest in Scottish geology, so may have been a Scotsman......

Mystery Microscopist

2011-09-30T22:29:00.000+01:00

Many years ago, when I was a student, I was given this box of old prepared microscope slides. I can't remember who the donor was but they've been at the back of a cupboard for years and only emerged when I was having a clear-out, a couple of months ago.

They date from around the time of the First World War. Some were commecially prepared by the firm of Watson & Son, of 313, High Holborn, London - labelled with beautiful handwriting, in mounts that were so well ringed with shellac that they have remained in perfect condition for almost a century.

Others were prepared by the original owner, who I'm guessing must have been a chemist because many are cystalised mounts of chemical compounds, intended to be viewed with polarised light, made from substances that would only have been available to a professional chemist - possibly a plant biochemist because quite a number of the crystals are naturally-occuring plant compounds that he might have extracted and purified himself. One contains the only clue to the identity of the mystery microscopist, because he has written his name in chemical crystals on the slide - 'SID'.

Sid would have looked at these specimens with a rather primitive instrument called a Fox Polariscope - so Sid probably wouldn't have seen the images in quite the same vibrant colours that you can see here, achieved with a modern polarising microscope. The specimen above is strychnine...

... this is floridzin, an alkaloid from apple roots...

...as is this one, too.

This is mercuric cyanide

Salignin...

Coumarin, the compound responsibe for the scent of new-mown hay...

Salicin, extracted from willow bark and the precursor of salicylic acid ,better known as aspirin...

... and ammonium bitartrate

Hooked on Hops

2011-09-23T21:01:00.000+01:00

Hops Humulus lupulus have an impressive ability to climb supports - either up other plants or, in the case of cultivated hops, up poles in hop gardens. Charles Darwin devoted a lot of time to studying the way in which their shoot tips rotate as they grow (by the process of circumnutation), seeking out objects to coil around (you can read more about his experiments here). There's more to hops' climbing ability than circumnutation and rapid growth, however - their stems are clothed in very distinctive epidermal hairs (trichomes) that act as grappling hooks, securing their grip on supporting structures.

The hop trichomes that are adapted for climbing have a very distinctive anvil shape - you can see them here, at low magnification, on either side of a hop leaf petiole.

At higher magnification the anvil shape is very distinctive, something noted ....

.... by the botanist Anton Kerner von Marilaun in his Natural History of Plants (1895).

Hops have been cultivated for centuries, primarily for the resins produced by their epidermal glands, mainly at the base of the bracts in the female flowers but also on other parts of the plant, including the underside of the leaf. In the photograph above you can see the minute gold drops of resin on the lower surface of a hop leaf. The resins are converted to bitter isohumulones during the brewing process, adding a distinctive flavour to beer.

Bacterial Root Nodules

2011-08-22T12:40:00.002+01:00

These are bacterial root nodules on the root of runner bean Phaseolus coccineus. Each nodule contains a population of Rhizobium bacteria that are capable of converting atmospheric nitrogen into soluble forms of nitrogen that the plant can use for growth - which is what makes this symbiotic association between plant and bacterium so valuable for agriculture. In annual legume crops, once the bean crop has been harvested the root nodules decay and release nitrogen in the soil, where it can give a yield boost to following non-legume crops in the crop rotation - like wheat, for example.

In this image one of the nodules has been cut in transverse section and stained with the fluorochromes calcofluor and auramine O. The plant root, with its xylem vessels visible, is at the top. The bacteria filling the root nodule, encased in blue-stained plant cells, are stained yellow. The Rhizobium bacteria in the soil penetrate through a root hair, trigger proliferation of the host plant root cells to form a nodule and multiply within. Healthy root nodules are pink when you cut them open due to the presence of leghaemoglobin which, like haemoglobin in mammalian blood, absorbs oxygen. This is important because oxygen would otherwise inhibit the enzymes in the nodule that 'fix' nitrogen into soluble forms. Bacterial nodules that are not pink when you cut them open are likely to be parasitic on the host plant, rather than symbiotic.

This is the difference that nodulation makes. The plant on the right has effective nodules, the one on the left doesn't. The interaction between plant and bacterial strain is complex; for any give crop cultivar, different bacteral strains will show varying degrees of effectiveness in boosting crop yield and different crop varieties perform best with different bacterial strains. Deliberately inoculating seeds with effective Rhizobium strains can produce significant yield benefits, although there is no guarantee that any particular inoculum will persist in a soil type or location where it's not a naturally-occurring strain amongst the existing soil microbial community.

Out of Sight,Out of Mind...

2011-08-10T21:57:00.000+01:00

Roots are the most neglected parts of plants, perhaps because they are out of sight and - superficially at least - lack the intrinsic aesthetic beauty of the above-ground parts. For most (although not all) plants they are vital structures and - when you look really closely - they have an intricate beauty of their own.

Root tips are sensitive gravity detectors, ensuring that the root always grows downwards into the soil. This root was held in the horizontal plane for less than an hour before it redirected its growth downwards. Behind the root tip you can see the point where the root hairs develop, with newly initiated root hairs just visible nearest the root tip but becoming longer as you move away from it. Further back still the root hairs die away continually and each has a life span of just a day or two, but they are continually replaced as the root penetrates further into the soil. The passage of the root through the soil is assisted by lubricating mucilage produced by the root tip, whose surface cells slough off. The mucilage also supports a bacterial microflora that helps the root acquire nutrients and may provide some protection from disease-producing organisms.

This is a root tip sectioned vertically and stained with a fluorescent dye called DAPI. If you click on the image to enlarge it the details will be a little clearer. The brightly fluoresescing dots are the nuclei, one per cell, and you can see the files of cells produced by sequential cell division followed by cell elongation, which pushes the root ever-further into the soil.

This is a root in transverse section, further back from the tip than the previous image, in the middle of the root hair zone. It has been stained with a fluorescent dye called calcofluor, which makes the cellulose cell walls fluoresce blue in ultraviolet light. From the outside inwards, you can see the long root hairs, each a single cell that arises from the root epidermis (surface layer of cells). Next inwards lies the root cortex, which constitutes the vast bulk of the cells, then in the centre you can see the stele - the cylinder of vascular tissue that transports water upwards to the rest of the plant and carries sugars and amino acides downwards to support the continued growth of the root.

The arrangement of the various cells and structures is more clearly visible here, at higher magnification. The large circles in the stele, top left, are xylem vessels that conduct water away from the root.

The root hairs, which are in intimate contact with the soil particles, absorb water and soluble minerals that are transported through the root cortex, both from cell-to-cell within cell cytoplasm (the symplastic route) and through cell walls and the spaces between cells (the apoplastic route), to the stele in the centre of the root.

Once the water reaches the stele it encounters a single layer of cells called the endodermis, that sheaths the stele. The walls of the endodermal cells contain a substance called suberin which renders them impermeable, so water that arrived via the apoplastic route is forced into and through the cytoplasm of these cells, where dissolved minerals are selectively removed. You can see the suberin deposits, known as the Casparian strip, as the orange staining in the single ring of cells that lies between the blue and the yellow cells in the section of a stele above. Some water also passes unimpeded through specialised passage cells in the endodermis - if you follow the ring of cells with the orange stained Casparian strip in their cell walls around the stele in the image above, you'll notice a few passage cells with no orange-stained suberin deposit in their walls.

Almost all the water taken up and transmitted via both routes, via the cytoplasm of the endodemis cells or via their passage cells, then enters the dead xylem cells that carry it aloft in the water column that is drawn upwards by transpiration from the leaves.

When gardeners buy plants in garden centres there's a great temptation to simply dig a hole and plant them, without teasing out the pot-bound roots or cultivating the soil around the planting hole, but a little tender, loving care for root systems pays great dividends: the vigour of the plant above the soil depends on the health of the roots, hidden below the surface.

Banana Stellate Parenchyma

2011-06-18T21:18:00.000+01:00

These beautiful cells come from the midrib of a banana leaf. Each is shaped like a 6- or 7-armed star, with its arms joined to the arms of surrounding cells, forming a lattice of cells. This form of tissue is known as stellate parenchyma and you can find another example here. The image was produced using polarised light and the brightly coloured birefringent objects inside the cells are calcium oxalate crystals inside the cell vacuole. You can see further examples of calcium oxalate crystals, including a video of their Brownian motion inside a cell, if you click here.

To find these cells you need to look inside the midrib of a banana (Musa sp.) leaf .....

by cutting transversely across the midrib, which reveals this internal pattern of strenthening tissue filled with very delicate, transverse plates of glassy cells ....

... then dissect out one of these plates of cells and mount it on a microscope slide.

Life in 10 Drops of Water: Assorted Protists and rotifers

2011-06-14T22:27:00.000+01:00

This is the fourth in the series of images of some of the organisms found in just a few drops of water collected from a pond in a disused quarry on the edge of the moors in Weardale.

An amoeba. I could spend a long time watching these - it's rather relaxing watching an organism whose motto for life must be 'go with the flow'

It seems to have ingested a wide varieties of objects.

This is one of the free-swimming ploimate rotifers, with tails that look like scissors - possibly Monommata caudata...?

Vorticella - a ciliate protist on a stalk, that contracts like a spring when disturbed. The green object is a cyanobacterium - possibly Gloeocapsa.

A ciliate protist that creeps along using strange 'whiskers' - and also swims very actively using smaller cilia. You can see a contractile vacuole quite nicely here. I think this, and the three below, might all be Oxytricha.

All three of the above ciliate protists look rather well fed - full of undigested algae.

This beautiful object is the flask-shaped shell of the testate rhizopod Cyphoderia ampulla. The amoeba that lived inside has long-since died.

This might also be the shell of a testate rhizopod ..........

... at higher magnification you can see that it's constructed of tiny translucent particles....

... that are especially fine and fit together beautifully around the orifice

.... and finally another heliozoan, that appears to be ingesting something

Life in a few Drops of Water:Dinoflagellates

2011-06-05T20:27:00.000+01:00

This is the third in the series of images of some of the organisms found in just a few drops of water collected from a pond in a disused quarry on the edge of the moors in Weardale

This little object (which I think may be a species of Peridinium), a mere five one hundredths of a millimetre across, is a dinoflagellate - a single-celled, hardshelled organism that's powered by two rapidly undulating flagellae. One runs on the horizontal groove around the 'equator' of the example you can see here. The other runs in vertical groove, extending from the equator to the apex - it's out of sight on the distal side of this image, although you can just see the apex of the vertical groove at the top. It seems like an unlikely means of motive power but it works - this one whizzed all over the slide before it paused for long enough for me to get a photograph.

This is the empty shell of a dead dinoflagellate, which reveals the intricate pattern on the armoured surface composed of cellulose plates. Unfortunately....

....it wasn't intact - you can see where about a quarter of the sphere has broken away, but you can also see the equatorial flagellar groove rather nicely. The green object approrach from lower right is a diatom, which is just about to punt the diatom out of the way as it glides past.

For some fascinating recent research on dinoflageelates, take a look at this post about a predatory dinoflagellate at Jennifer Frazer's The Artful Amoeba web site, where you can read about their amazing biology and also find links to drawings and electron micrographs that show the organism rather more clearly than my photographs.

Coming next: An assortment of protists

Life in a few Drops of Water: Desmids

2011-05-22T08:49:00.001+01:00

This is the second in the series of images of some of the organisms found in just a few drops of water collected from a pond in a disused quarry on the edge of the moors in Weardale.

This is a desmid - probably a species of Cosmarium. Desmids are typically constricted in the centre of the cell to form two mirror-image halves.

These are single-celled, photosynthetic algae that often have a patterned cell wall that's ...

.... most clearly visible after the cell has died and lost its chlorophyll.

This appears to be one half of a desmid that has broken at the bridge joining the two halves (known as the isthmus), revealing the fractured hole.

Coming next: Dinoflagellates

Life in a Few Drops of Water: Diatoms

2011-05-10T22:42:00.003+01:00

A few days ago, when we were out walking in Weardale, I collected a small sample of water from a pond in a disused quarry on the edge of the moors, then spent several hours that same evening exploring just a few drops of the pond water - maybe ten in total - under the microscope. The organisms pictures in this post are all diatoms - minute photosynthetic organisms encased in a shell of pure silica that often bears the most intricate pattern on its surface. This one, caught in the act of dividing, is Pinnularia.

Some are long and thin (this is Nitzchia sigmoidea), while.....

....others are joined together in chains.

Navicula? When diatoms die their silica shell remains, almost indestructible, and in that transparent state, with no contents, the full beauty of the sculpturing on their shells can be appreciated.

The pattern of fine ridges on Cymbella tests the ability of microscope lenses to resolve such fine detail.

Diatoms generally move in a gliding motion through the water but sometimes they can be attached to a substrate via mucilaginous stalks.....

... seen here at higher magnification.

Most of these organisms are less than one twentieth of a millimetre long.

Coming next: Desmids....mirror-images in miniature

Give Me Strength

2011-04-28T17:26:00.000+01:00

This cross section of the stem of a soybean seedling shows the early stages in a developmental process that will produce a stem capable of supporting the mature plant. I stained the section with two fluorescent dyes - calcofluor, which binds to cellulose cell walls and fluorescences blue in ultraviolet light and auramine O, which binds to lignin and fluorescences yellow. It's the lignin laid down in cell walls that gives the stem the strength it will need to support the leaves and flower.

Working from the bottom left-hand corner towards top right, the core of the stem is filled with blue, thin-walled pith cells, which are simply packing tissue. Some of these have become slightly lignified and are fluorescing yellow and some, that are arranged in vertical rows of between two and five cells have distinctly thicker walls - these are xylem vessels, which are dead cells that form tubes that conduct water up the plant from the roots.

Above those lies a broad band of blue-fluorescing thin-walled cells that are very small and arranged like piles of bricks. This is the cambium - the plant's stem cells that divide continuously to produce new xylem on the inside and new phloem elements on their outer surface. The small, bright blue-fluorescing cells on the outside of the cambium are the phloem sieve tubes and associated companion cells, which conduct sugars produced by photosynthesis in the leaves to other parts of the plant.

The sinuous layer of yellow-fluorescing cells above the phloem are becoming lignified and these will contribute major structural rigidity to the stem as it grows, forming a continuous cylinder inside the stem. Outside of these lies the stem cortex, with blue cells becoming smaller in the layers just below the epidermis - and then the outer epidermis of the stem is covered in the yellow-fluorescing cuticle, which restricts water loss and defends that plant against pathogens.

At the stage when this section was taken the stem was about 3mm. in diameter and about 10 centimetres tall.

Swallowed by the Sun Animacule

2011-04-23T20:41:00.000+01:00

I've long been fascinated by heliozoans aka 'sun animacules' and have posted on them before, but thought I would again because I've captured some pictures of one without squashing it under a coverslip - and also photographed it digesting its last meal. Briefly, heliozoans are single-celled amoebae which, instead of flowing around and engulfing their food with cytoplasmic arms called pseudopodia, radiate spines of cytoplasm supported by an internal scaffold of microtubules. They roll through the water like a one-tenth-of-a-millimetre-in-diameter sea mine, bringing dead to anything small that contacts those spines. This is a through-focus sequence of this microscopic protist menace, so in the image above we are looking down on the upper surface, onto what looks like a sphere of cytoplasm radiating needles in every dimension...

.... and here the focus has moved down a bit, onto the surface of that cytoplasm, which is broadly divided up into a pattern of hexagonal blisters....

.... and now we are looking at the contents of its central food vacuole - and this heliozoan has somehow managed to ingest a testate rhizopod - a form of amoeba that lives in a shell shaped like a hot air balloon. Incidentally, all the pictures on this post will be clearer if you double-click on them to enlarge them in a separate window. Below is the same sequence, but this time at x400 magnification instead of x100......

..... so here are the surface hexagons, with the base of those lethal radiating spines....

..... and here is the blistered pattern - which looks like cells but this is a single-celled protist - so they must be formed with the aid of microtubules, I guess ......

.... and here's its food vacuole, with ingested testate rhizopod. It will digest the cytoplasm of its prey and spit out the empty shell.

It's easy to loose a sense of scale when peering down the microscope at small organisms - a sense of their place in the universe. So the picture above shows the place where this 100 micron predator came from - from the moss around the edge of this small pool on bleak moorland in Weardale, County Durham . The pool is about a metre long, so if you lined up 10,000 heliozoans spine-tip-to-spine-tip they'd stretch from one end to the other ....

..... and that tiny pool is somewhere in the middle distance in this landscape ......... and beyond that the solar system and beyond that the universe, home to an exquisite tiny life form that has been rolling through our planet's water, ingesting whatever it touches, for well over a billion years. Time travel is possible if you have a microscope....

Newly-hatched Snails

2011-04-05T22:03:00.000+01:00

A couple of weeks ago I posted some pictures of garden snail eggs that had been found by Chantelle Kerr, one of our research students, that showed the calcium carbonate crystals in the egg shells. Well now she has hatched them out and here they are ....

Each is about the size of the head of a dressmaker's pin, less that 2mm. in diameter, and the shell is translucent so you can see the snail's organs inside. I think the yellowish blob at the top of the shell might be the digestive gland. This one is taking a cautious peek out from under the shell, at the scary world outside ...

... checking that the coast is clear.........

........ and making a dash for safety.

It seems that they ate the egg shells when they emerged, so all those calcium carbonate crystals have now been recycled into that translucent shell.

If it survives to adulthood, this is what it'll look like. There go the lettuces....

Micro-rock-pooling: an Intertidal Insect

2011-04-04T12:14:00.000+01:00

There aren’t many insect species that live in the intertidal zone. The two you’re most likely to encounter are the springtail called Anurida maritima that scoots across the surface of rock pools on the upper shore and seaweed flies Coelopa frigida that breed in vast numbers in the rotting heaps of seaweed that pile up on the strandline. Even fewer insects complete their life cycle actually submerged in salt water but one is this little chironomid midge called Clunio marinus, that I found amongst the fronds of Cladophora seaweed in rockpools on the beach at Whitburn near Sunderland yesterday.

This specimen was about 5mm. long and living in a tube constructed from fine sand grains amongst the fronds of the seaweed.

It fed by hauling itself through the branches of the seaweed using two short leg-like appendages just behind the head.

The midge larva seemed to be nibbling away at much smaller organisms that encrusting the fronds, using a pair of pointed jaws. As far as I could tell it didn’t eat any of the seaweed – just the organisms that encrusted it.

Chironomid midges are extremely common in fresh water, breeding in vast numbers on ponds and even in small bodies of water like waterbutts in gardens. This species, though, as evolved to survive the rigours of life in salt water rockpools on the middle and upper seashore, where temperature and salinity levels can be extremely variable.

You can find a web site devoted to chironomid midge biology here

Snail Eggs

2011-03-19T18:25:00.000Z

Some of our project students have been working on the feeding habits of garden snails Helix aspersa and one of our postgrads, Chantelle Kerr, drew my attention to the fact that some of their snails had been laying eggs in the tanks where we were keeping them. I was hoping to see some signs of the developing embryos when I took a look at these under the microscope, but the eggs were disappointingly cloudy. But then, on closer examination, the 'cloudiness' turned out to be something rather interesting. Take a look at the eggs on the microscope slide above and you can just about see clusters of white specks inside them (double click for a larger image), especially in the two at the back.

These turned out to be vast numbers of calcium carbonate crystals, embedded in the outer gelatinous egg capsule. The purple background colour is the result of using a colour filter to improve the contrast - not the real colour of the egg interior, which is colourless.

At higher magnification you can see that some crystals are simple cubes, while others are aggregated together. What are they for? Well, a quick search of the web reveals that the embryonic snails use this store of calcium to produce their first shell - the parent snail provides them with a supply of building materials for a shell when it lays the egg. You can read more about the chemistry of snail shells by visiting the excellent Snail's Tales blog.

Microscopic Living Do-nut

2011-03-02T22:02:00.001Z

Here's another interesting organism that lives in the temporary pools of water, known as phytotelmata, that accumulate in cavities in the surface roots of beech trees. It's a testate rhizopod - an amoeba that lives in a shell that it secretes - and is called Arcella. It's about a tenth of a millimetre in diameter. The shell in old specimens tends to be brown but this one is nicely translucent, revealing the exquisite sculptured pattern that decorates its surface.

Here's the flip-side, showing the hole in the underside of the hollow do-nut shaped shell and...

... here, with a shift in focus, you can see the amoeba inside, with one arm or pseudopodium protruding out of the hole. The dark structure that you can see in the cytoplasm is a vacuole filled with carbon dioxide - the organism produces one of these to increase its buoyancy when it needs to float up to the surface.

Here you can see the whole organism inside the shell in side view, poised above the hole. The circular structure in the cytoplasm, top left at about 10 o'clock, is a nucleus.... the control centre of the cell.

There are always two nuclei in the cytoplasm of each Arcella.... so which one is in control? Who knows?

And finally, here it is on the move, extending a pseudopodium that it uses for locomotion and food capture.

This is probably Arcella discoides. If you'd like to see some wonderful illustrations of more testate rhizopods take a look at this page, where you'll need to double-click on the images to enlarge them.

Teeming Millions - Paramecium Population Explosion

2011-02-16T06:18:00.000Z

Well, teeming thousands anyway. These little organisms are Paramecium, single-cells protists that swim with incredible speed using ciliary hairs on their surface, that beat in rhythm. Here they're magnified one hundred times. This single drop of water on a microscope slide probably contained about five hundred...

... and this little pool of water, trapped in a cavity formed by the coalesced roots of a beech tree, must have contained millions, feeding in bacteria and other microscopic organisms that were in turn feeding on the rotting leaves trapped in the water. The pool is fed by rivulets of water that trickle down the trunk when it rains. Temporary pools of water trapped in plants like this are known as phytotelmata. The best-known examples are the pools of water trapped by the leaves of bromeliads (urn plants) that grow as epiphytes in the rainforest tree canopy. They host all sorts of exotic animals - tree frogs, land crabs, dragonflies - but this beech tree-root equivalent hosted nothing larger than rat-tailed maggots - the larval stages of drone flies. But while the species diversity in the beech-tree pool might have been low, the sheer abundance of the Paramecium was staggering.

Here they are magnified two hundred times. The circles that you can see in some of them are contractile vacuoles, that constantly expell water from the cell cytoplasm.

At 400 times magnification you can see the fine cilia (top right) that are arranged in rows over the surface of the cell - you can just make out their dark parallel lines and you can also see algae that the Paramecium has ingested, inside the cell.

Static images don't really do justice to the helter-skelter movement of these little protists, but the video clip below gives some impression of what is going on in those little temporary pools of water trapped by the tree roots.

Micro-rock-pooling

2011-01-16T20:07:00.000Z

This is probably the low point of the year for exploring life in seaside rock pools but if you search amongst the fronds of seaweeds like the red Ceramium and green Cladophora, that can still be found on sheltered parts of the shore, and take them home for microscopic examination you can still find a wealth of marine life in miniature. Here, beautifully camouflaged in a flecked green exoskeleton, is a sea slater Idotea sp.

The multi-facetted compound eye of Idotea is exceptionally beautiful.

In amongst the weed and hanging from the surface film in the rockpool you'll almost certainly find large numbers of juvenile gastropod molluscs, each only a couple of millimetres long - this one is almost certainly a Littorina (winkle) species. Notice the single dark eye at the base of each antenna.

Acarine mites are incredibly diverse animals that live in almost every habitat imaginable (click here for more information on them). Scores of these little 8-legged animals, each only about a millimetre long, were scurrying around amongst the seaweed fronds. Not much is known about the ecology of marine mites, which mostly belong to a single family - the Halacaridae. Notice the long, hooked claws that stop them from being washed out of their seaweed shelter, and the piercing mouthparts at the head end. There's a short video clip below.

You can find more on freshwater marine mites here.

Nature's Stained Glass Windows

2010-12-24T22:37:00.000Z

Season's Greetings and Best Wishes for 2011 to all readers of this blog

Looking like a stained glass window, this is the remains of the seed pod of one of last summer's garden flowers, Lunaria annua (commonly known as honesty, because the dry seed pods resemble silver coins), magnified around two hundred times and viewed using polarised light.

When honesty seed pods ripen they are flattened and composed of three components. Imagine three large 'coins' joined to each other all around their rims, with the central 'coin' attached to the plant via a stalk. Swelling seeds are attached to the rim of both faces of the central 'coin' via their own slender stalks, visible when sunlight shines through the whole structure.

When the pod dries out and ripens the tensions in the drying, contracting cells of the walls of the 'coins' tear them apart around their rims, so the two outer 'coins' detach and flutter away in the breeze, followed by the winged seeds, leaving the central 'coin' attached to the dead plant and surviving deep into winter.

These are the cells of that central, surviving 'coin' magnified about one hundred times and using ordinary white light....

... and these are the dazzling interference colours generated when polarised light is used.

At two hundred times magnification it's clear that the 'coin' is formed from two layers of cells, orientated at different angles, so that the tensions they develop when they dry will twist and distort the 'coin' and help to rip apart the sutures with the outer 'coins'.

At four hundred times magnification you can clearly see the pores through the thick cell walls which were the plasmodesmata - the channels of communication between the cytoplasmic contents of one cell and the next, while the whole structure was still alive and the seeds were still developing.

The dry, dead cells form intricate patterns...

... whose colours change as they are rotated in the plane of the polarised light.

The Colour Purple

2010-12-18T21:40:00.000Z

This rather beautiful flower is Tibouchina urvilleana and the purple of its petals is due to the presence of anthocyanin pigments, which are dissolved in the cytoplasm of the petal cells.

If you magnify the petal surface about 200 times you can see the way in which the petal cells fit together, like pieces of a jigsaw puzzle. This piece of petal is mounted in water but if it's transferred to a concentrated solution of sugar ...

... the water in the cell begins to flow out through the semi-permeable cell membrane by the process of osmosis, with water travelling out from the less concentrated solution in the cell to the more concentrated solution surrounding it. Within a few minutes spaces become visible between the cytoplasm and the cell wall, where the cytoplasm shrinks ....

... and within a few more minutes the cytoplasmic contents of the cell have shrunk even further, so the purple anthocyanin pigment becomes even more concentrated in the remaining cytoplasm.

While I was looking at the petals I noticed something unusual around their edge - a fringe of microscopic hairs, invisible to the naked eye.

Each hair is tipped with a glandular head.

... that looks as through it may contain oils.

What are these hairs for? Secreting aromatic compounds that attract insect pollinators, perhaps?

Sticky Jack

2010-12-03T15:14:00.000Z

This is a cross section of the stem of the plant commonly known as goosegrass or sticky Jack and more scientifically as Galium aparine. Sticky Jack is a very common weed that scrambles up through other vegetation using its covering of hooked hairs on the stem and leaves and which sticks to clothing with these when kids throw handfuls of the stuff at each other.

This image was produced using fluorescence microscopy, staining the cells with compounds that bind to the cell walls and fluoresce. The blue cells have walls made of cellulose and their blue fluorescence is due to the calcofluor that they've been stained with, which fluoresces blue in ultraviolet light. Calcofluor has been used as a 'blue whitener' in washing powders - it binds to the cellulose in cotton fabrics and fluoresces faintly blue in the UV component of sunlight. The yellow staining is due to another fluorescent dye (fluorochrome) called auramine O, which binds to cutin in the outer cuticle of the plant, and to dead, lignified cell walls that give the stem its strength - and it fluoresces yellow. The cuticle in this cross section is the thin yellow line covering the outer surface of the section. The yellow circle in the centre is composed of dead, lignified cells - not particularly well developed in goosegrass because it scrambles over surrounding vegetation rather then investing resources in producing a stout lignified stem of its own.

Strings Attached

2010-11-27T20:10:00.000Z

Deciding on the prime time to pick a bean pod is s tricky business. Leave it too late and the pod will become tough and stringy - and the reason for that is because as it grows the pod begins to prepare to shed its seeds. Members of the pea family - the leguminosae - carry their seeds in pods that naturally become brittle when they dry and ripen, when tensions developed along the suture between the two pod halves and in the pod wall eventually become so great that the pod splits open violently, hurling out the seeds. Plant breeders have worked hard to breed this trait out of legume crops, but species like runner bean still produce long strands of woody, lignified cells in their pod walls as they ripen. In this fluorescence micrograph, showing a cross section of the upper suture of a developing pod, the bright yellow arcs of cells at the top are the 'strings' that you need to strip out of the pod before you eat and cook it if you've left it too long before harvest. The yellow cells just creeping into the picture at bottom left belong to the parchment layer that develops in the pod wall. Together, these thock-walled cells develop the tensions in the pod as it dries that will eventually split it open along its longitudinal sutures and release the seeds.

Twister

2010-11-22T19:50:00.000Z

To appreciate the true beauty of mosses you really need to explore them with a hand lens or low power microscope. This is Tortula muralis, wall screw-moss and to find out how it acquired that colloquial name you need to take a close look at the spore capsules.

Wall screw moss grows in the mortar-filled cracks in walls, where it produces spore capsules that are carried aloft on stalks that are a couple of centimetres long at maturity. These are capsules in the very early stages of development, before their stalks lengthen, but if you take a really close look at a mature spore capsule....

...it looks like this. Notice how the capsule's stalk (seta) has twisted helically. If you take a close look at the capsule (double click on the image for an enlarged version) you can see that most of it is sheathed in a membranous covering - the calyptra. Gently pulling this off with a pair of forceps reveals....

... a lidded capsule underneath and if you pull the lid (operculum) away....

... it reveals a screw thread-like arrangement (the peristome) underneath, that gives the moss its common name. These threads twist up tightly in moist air but untwist in a dry atmosphere, allowing the minute spores to be shaken out when the seta trembles in the wind. In this image you can see that the operculum that has been removed has become temporarily stuck to the base of the capsule - normally it will just fall away.

Control Centre

2010-11-11T21:19:00.000Z

This is a cell from a developing seed cotyledon of a broad bean Vicia faba plant. In the centre you can see the nucleus, floating like an icy-blue planet in a universe of cytoplasm - mission control, home the the DNA molecules that encode all the instructions for making the cell and, indeed, the whole plant. I stained the cell with a fluorescent dye that binds to the DNA in the nucleus and fluoresces blue when it's illuminated with ultraviolet light - the DNA (chromatin) is visible as the bright blue flecks on the nuclear membrane. The large, brightly fluorescing spot inside the nucleus is the nucleolus, where DNA is transcribed into ribosomal RNA subunits that are transported out of the nucleus and assembled into ribosomes in the cytoplasm. There the ribosomes form part of the machinery that translates the genetic code carried by messenger RNA, which is transcribed from the DNA in the nucleus, into proteins that are assembled from amino acid subunits. The nucleolus is highly visible in this cell because cotyledon cells in the seed manufacture and store proteins that are used when the seed germinates, to support the early growth of the seedling; this is a very busy nucleus and nucleolus because at this stage the cell is making a lot of protein. During early cotyledon development the cells are loosely packed together and you can see large triangular intercellular spaces between them. Later these will disappear, as the cells become packed full of proteins, lipids and starch, the cell walls thicken and the seed dries out during the seed ripening process. N.B. The cell walls are fluorescing blue in this image because of their own inherent biophysical properties, not because they contain DNA like that which is fluorescing blue in the nucleus.

Trees: the Inside Story

2010-11-02T10:36:00.000Z

Almost as soon as plants colonised the land surface they began to compete for light, struggling to grow out of each other’s mutual shade. The ultimate solution, adopted by trees, was to produce woody stems and grow tall, shading out competitors below. It's a very successful strategy - left to their own devices, many terrestrial ecosystems where water and warmth are adequate become forests. These (above) are cross sections of stems of two sycamore Acer pseudoplatanus seedlings, just a couple of weeks after germinating from a seed in spring, and already they have begun to produce woody thickening in some of their cells, visible here as the bright yellow fluorescent staining inside the stem (on the periphery of the large pith cells in its core). The very narrow yellow fluorescent line around the perimeter of the stem is the waxy cuticle secreted by the epidermal cells that protects the young stem – just a couple of millimetres in diameter at this stage - from water loss and invasion by pathogens. Double-click on the image for a clearer picture.

Fast-forward almost three years now and this seedling has grown into a sapling. In this cross section of a three year old lime (Tilia sp.) stem the big cells at the core are the pith. The three concentric rings of brown cells outside of that contain the xylem vessels that conduct water up and down the stem. They’re dead and their walls are strengthened with woody lignin, producing a strong, rigid support for the fast growing shoot and leaves. The width of those annual rings varies according the growing season – but I suspect that the outer, most recent ring is narrower because this shoot was harvested for microscopic sectioning sometime in mid-summer, before that year's annual growth was complete. Take a close look at the outer edge of the outer annual ring of xylem (double click the image to enlarge) and you may just be able to make out a distinct narrow zone of very small blue-stained cells, just a few cells thick (at about 7 o'clock on the section). This is the cambium – the thin layer of living cells that divides to produce dead xylem cells on its inner face and living phloem cells, that conduct sugars from the leaves to the rest of the plant, on the outer side. Together the phloem and cambium are only a few cells thick and represent the most important living tissue inside the tree. Their protection is vital for the tree’s survival, so they are covered by a thick layer of bark tissue, also stained blue where the cells are alive but showing as grey-brown on the outer surface of the twig, where they are dying or dead. This is the tree’s waterproof, self-repairing, insulating, wound healing tissue, protecting the delicate living layer of cells inside. Growing tall by producing annual rings of growth is a long-term investment for a plant which only reaches full size after decade of growth, but the return on investment can then continue over centuries – and in some cases millennia - of annual flowering and seed production. As the stem adds annual rings, expanding in girth with every succeeding year, the outer dead bark layer splits into characteristic patterns, depending on the tree species. The line of red cells in the bark tissues are fibres - dead cells that strengthen the young stem.

More Smut - Sex-change in Campion Flowers

2010-10-18T10:16:00.000+01:00

A while back I posted some pictures of the smut fungus Microbotryum violaceum infecting the anthers of white campion .The flower above is a pink campion - probably a hybrid between white campion Silene latifolia and red campion Silene dioica - whose stamens are also full of the brown fungal spores. Both red and white campions exist as separate male and female plants. This fungus fills the anthers of male plants with its spores which are carried from flower to flower by pollinating insects, but it also brings about a change in the sex of female flowers, so that the female structures are suppressed and appendages called staminodes develop into stamen-like structures that produce the fungal spores and attract insects that are fooled into thinking they are collecting pollen grains. So, when the whole local population has been infected with the sex-changing smut fungus, how do you separate the genuine males from the gender switching females?

You need to look closely, under the microscope. If the 'stamens' are simply full of fingal spores, like those above, then you are looking a gender-switching female, but.....

...... if there are a few large pollen grains amongst the tiny fungal spores, then you are looking at a genuine male plant that was infected after the pollen grains began to develop.

Harvestman

2010-09-23T13:52:00.001+01:00

I found this delightful little harvestman amongst some raspberries that I picked yesterday evening. Although they are carnivores, they do seem to have a liking for ripe fruit.

Despite their spider-like appearance and the fact that they belong to the Arachnids, harvestmen are not true spiders but belong to an order of their own known as the Opiliones, distingished from spiders by their globular bodies, unlike those of true spiders which are divided into two parts - the separate thorax and abdomen, separated by a constriction. Harvestmen always seem to have an other-worldly appearance and, scaled up to monstrous proportions, wouldn't be out of place in a science fiction movie. Many of their sensory functions are located in their legs and if you watch the way in which they use these - particularly the second pair that are often far longer than the others - it's quite clear that they are using them to feel and taste their way around their habitat. Nevertheless, when danger threatens they can shed a leg (autotomy) and leave it twitching on the ground, to deflect the attention of a predator. Unlike true spiders, they can't regrow limbs after moulting, so this desperate measure leaves them short of a limb and sensorily deprived. Before they resort to limb-shedding, they often exude an unpleasant-smelling liquid from their leg joints which you can smell if you hold an irritated harvestman in your hand. This isn't an infallible deterrent - I've watched robins feeding their brood with harvestmen.

One of the most remarkable features of harvestmen is the arrangement of their eyes, in a kind of turret called an ocularium, high up on their back. This arrangement makes sense when you get down to a harvestman's eye-level ...

... when it's clear this this gives it 360 degree vision around and above its globular body....

..... although one can only guess at how much detail those unblinking black eyes resolve.

Nevertheless, whatever angle you approach from a harvestman always has it covered........one of those eyes always seems to have you in its sights...

There's an excellent little booklet called British Harvestmen by J.H.P. Sankey and T.H.Savory (Synopses of the British Fauna (New Series) No. 4 ISBN 0 12 619050) that not only provides fascinating detail about their biology but also contains some delightful little anecdotes. For example, some species apparently kill their prey by positioning their globular bodies over their victim that's imprisoned by their legs and then bouncing up and down on those long legs, 'pile-driving' the unfortunate prey. Others have been noted for a prediliction for marmalade sandwiches from a picnic and on one occasion ink from ink wells (although this one refused black ink and would only drink the red stuff).

I haven't got around to identifying the species of this individual yet and if there's anyone out there who can help me out, I'd be grateful....

Moth Pointillist Colour Patterns

2010-09-13T12:28:00.000+01:00

I found this herald moth Scoliopteryx libatrix, with these beautiful orange markings on its wings, in my garden.

The whole moth is covered with scales, of various shapes, sizes and colours over its whole body, even to the extent that its legs are clothed in this rather fetching pattern of alternating black and white rings.

The main body is covered with fine hair-like scales, but the scales on the wings are....

... much broader, although they vary in width and colour. One interesting feature is that the patches of colour that look fiery orange to the naked eye are composed of a mixture of pinkish-red scales interspersed with variable numbers of yellow scales. The whole effect is reminiscent of colours produced in Pointillist paintings, of the kind made famous by George Seurat. By Seurat's day (1859-1891) the study of colour had revealed that the close juxtaposition of points of two colours could produce the effect of a third colour when viewed from a distance and Seurat exploited this in his meticulously executed paintings. The computer monitor screen that you are viewing this blogpost on uses a similar principle, of coloured dots, to produce its vast range of colours. Butterflies and moths have been exploiting the same phenomenon for millions of years, to either make themselves conspicuous to mates or generate camouflage patterns.

The herald moth's wings also carry small clusters of distinctive white scales, like those just above the 'orange' patch here, which I suspect may be scent scales that emit pheromones recognised by other individuals of the same species.

Brittle Stars

2010-09-06T11:32:00.000+01:00

The swaying fronds of red seaweed that fringe rockpools near the low tide level on the seashore are home to a wealth of miniature marine life, less spectacular than the inhabitants of coral reefs but every bit as intriguing. I found scores of these tiny brittle stars, the largest no larger than a centimetre across (including arms), on a visit to the Northumberland coast at the weekend. Brittle stars, or ophiuroids, are relatives of starfish and sea urchins, in the phylum Echinodermata (which means spiny skin - a feature many members of the phylum share). The view above is of the underside of one of the brttle stars, showing the mouth fringed with five teeth formed from calcareous plates.

Seen from above, five arms radiate from the pentangular body. Each arm is formed from articulated segments linked by muscles and these are very flexible, so the animal often curls the tip of an arm around a seaweed frond to stop itself from being washed away by currents. If it's alarmed the muscles between the arm segments contract and then the arms become very brittle.....

... and it doesn't take much force to snap them, as has happened here with the upper arm. This is not a problem, as....

... arms can easily be regenerated, as is happening here with the middle, lower arm. This capacity for shedding and regenerating arms is analogous to the way that lizards shed their tails (autotomy) if they are picked up by that appendage.

At higher magnification you can see the anatomy of the arms more clearly. Each calcareous segment bears spines and a pair of tube feet, that are all interconnected by a hydaulic system of radial canals that run along the arms and a ring canal that runs around the central body. Local relaxation or contraction of muscles, compressing liquid within, elongates or retracts the tube feet.

Unlike the tube feet of starfish which have suckers on their tips and are used for 'walking', those of brittle stars are primarily for sensory purposes and to assist in feeding, by secreting adhesive mucus. In this higher magnification image you can see that the tube foot is hollow.

The ring of tube feet around the mouth on the underside, where the arms converge, help to sweep food particles beyond the five calcareous teeth)....

.... into the muscular oesophagous, and then into ....

... the stomach. The tiny central body also contains gonads, that produce eggs and sperm that give rise to the planktonic ophiopluteus larvae.

When they're fully grown some brittle star species can reach 60 centimetres in diameter (not in Britain, though), but they all begin life as planktonic larvae, often settling into the shelter of seaweeds on the nursery slopes of rock pools or coastal shallow seas, which are of such importance for the health of the oceans.

You can see a YouTube vieo sequence of an adult brittlestar here.

Plant Plumbing

2010-09-02T22:03:00.000+01:00

Swiss cheese plant Monstera deliciosa is commonly grown as a decorative house plant but in its native Mexican rainforests it's a rampant climber, using its adventitious roots to cling to trees and climbing in much the same manner as ivy in temperate woodlands. Those holes in the Monstera leaf, whose resemblance to holes in Swiss cheese account for its name, let flecks of sunlight filter through to the layers of leaves below, all of which are transpiring water from their surface. If you cut a section through the stem, you can see the internal pipework that conducts water from the roots to the leaves.

In this transverse section of adventitious root, stained with fluorescent dyes that colour dead, woody cell walls yellow and living cellulose cell walls blue you can see the various cells that conduct liquids up and down the root. Embedded in that thick-walled strengthening tissue that gives the root (which in this case is used for clasping tree trunks and branches - this plant is a tropical climber) rigidity and are fluorescing yellow, are large vessels that conduct water in a continuous tensile column from the roots to the leaf, pulled upwards by evaporation from the leaf surface. The smaller tubes, lined with a layer of blue-fluorescing cell walls, may be resin ducts. The outer cells on the left, part of the ring of small bundles of living cells that encircle the root, are the phloem cells that conduct sugars manufactured by photosynthesis in the leaf to other parts of the plant. Swiss cheese plants are such familiar items of interior decor that they hardly attract a second glance, but they have extraordinary hidden beauty, only visible under the microscope

Defensive Weapons

2010-08-13T13:38:00.000+01:00

The outer layer of cells on a plant's surface - the epidermis - is the first line of defence against herbivores, pests and diseases so it's not surprising that many plants are covered with an array of defensive weapons. Sometimes these are cells that secrete repellent biochemicals, which give many plants a characteristic aroma when you brush their leaves. Other species have mechanical barriers, in the form of dense coverings of hairs (trichomes) to deter small insects like aphids. Stinging nettles are covered in a forest of complex stinging hair cells, each mounted on a pediment of cells. You can see some further, more detailed images of the structure of the stinging hairs here, but the image above is an aphid's-eye view of a nettle leaf underside - although they wouldn't see it in these lurid colours, which I generated using polarised light.

Gastrotrich

2010-08-04T18:25:00.000+01:00

I've been struggling to capture a decent image of a gastrotrich for quite a while, but this afternoon this obliging example (Chaetonotus sp., I think) paused just long enough in my field of view for me to record it. Gastrotrichs are miniature aquatic equivalents of the roadrunner, always on the move - although in this case propelled by a layer of beating cilia on their underside (gastrotrich means 'hairy stomach') rather than legs. This one seemed to be feeding. That circular mouth, surrounded by a ring of tiny teeth, and the muscular pharynx that it leads to ingest just about anything that the animal collides with and that's small enough to enter the gap. The outer covering of cuticular spines give this gastrotrich a fearsome appearence and if you are smaller that it is (i.e. less than about a quarter of a millimetre) the sight of one of these high-speed hunters hurtling towards you must be a nightmare - not that pond life suffers from nightmares; sorry, lapsed into anthropomorphism there. Been watching too many horror movies.

This specimen came from the edge of a Phragmites reed swarm, amongst the rotting debris in shallow water - a favourite habitat for gastrotrichs. You can see here how agile they are, capable of turning in their own length through 180 degrees. Those two appendages on the tail are adhesive organs. Gastrotrichs do sometimes rest and when they do they glue themselves to something convenient with adhesive secreted from the tips of those appendages. When they are ready to go again they secrete a releasing agent - that, and the glue, which both work under water, must be very interesting substances.

Pond scum

2010-07-12T21:44:00.000+01:00

Three weeks of warm weather had left my pond covered with large slimy masses of 'blanket weed' or 'pond scum', the filamentous green algae that tend to plague ponds that have too much nitrogen in the water. When I'd fished most of it out I took a look at a few filaments under the microscope and - like so many living organisms - it revealed structures of great beauty when it was magnified a few hundred times. Inside each cell in the filament the chloroplasts were arranged like strings of green pearls. Various filamentous algae have chloroplasts in different conformations and the most familiar is the spiral chloroplast in Spirogyra..... but this is a different genus.....

The series of fine rings that you can see around the bottom of the upper cell on the left here, just above its junction with the cell below it, identify this alga as a species of Oedogonium. A ring forms each time a cell of this genus divides, so this cell appears to have divided three times.

In amongst the algal filaments there were also desmids - this crescent moon-shaped example is Closterium. The clear areas at the tips of the 'moon' are vacuoles, that contain insoluble crystals of calcium sulphate - a diagnostic feature of this genus.

The most interesting alga in my pond, however, was this one - Coleochaete. It may look like just a pad of simple cells (with some of them apparently dead) but this is an organism of great evolutionary significance. Modern molecular biological studies, and comparative investigations into the ways in which cells divide in this species and in land plants, indicate that Coleochaete shares a common ancestor with present day land plants - mosses, liverworts, ferns, conifers and flowering plants. At some point - maybe half a billion years ago - algae like this, perhaps living in a warm pool of nutrient-rich water like my garden pond, started to colonise the mud and begin the long series of evolutionary changes that led to the development of today's terrestrial vegetation.

A discovery like this makes the chore of cleaning out the garden pond a whole lot more interesting..........

Rolling and Tumbling

2010-06-24T21:33:00.000+01:00

This colony of organisms is Synura, a member of the Golden or Chrysophyte algae, that I found in a water sample in the shallows of a reed swamp. Each member of the colony has a pair of unequal length flagellae (to fine to see at this magnification), whose constant beating sends the colony rolling and tumbling through the water. It's about a fifth of a millimetre in diameter. When high concentrations of Synura build up in water bodies they impart a fishy taste, posing a problem for the water industry.

A static image doesn't do justice to it, but the short video clip below gives a better impression of its constant movement.

Another Rotifer....

2010-06-15T21:48:00.001+01:00

I've posted pictures of rotifers before (here) but they are such amazing animals that there's always room for another - especially this one, which looks like a monster from a sci-fi horror movie. I found it at the edge of a pond today and it is - I think - a species of Euchlanis, which belongs to a group called loricate rotifers. A lorica is a hard outer shell (the word lorica is Latin for 'body armour') that provides protection and maybe has hydrodynamic properties that aid swimming. The protective function is evident in this photograph (above), where the animal's head is withdrawn into its shield-shaped lorica, which has claw-like points guarding either side of the opening. The animal is about a fifth of a millimetre long.

It may be that the shield-shaped lorica also functions like a wing, generating lift as the animal swims through the water, powered by a tuft of fast-beating cilia at the head end- which you can see beating in the short video below. When at rest the animal can anchor itself with its tail spines, which open and close like a pair of scissors.

These images were taken with differential interference contrast optics, which generate an apparent three-dimensional image of microscopic objects.

You can find out more about rotifers here.

Ahhhh-tishooooo!

2010-05-31T18:53:00.001+01:00

For hay fever sufferers, this can be one of the most miserable times of the year, thanks to grasses and trees that produce vast quantities of wind-borne pollen. Nevertheless, pollen grains are beautiful natural objects. The pollen grains above belong to a tropical plant called cup-and-saucer vine Cobaea scandens, which is pollinated by bats rather than by wind (do bats suffer from hay fever? Probably not...).

I stained the pollen with a fluorescent dye called acridine orange, which binds to the surface of the pollen grain and fluoresces yellow when you shine blue light on it - revealing this exquisite pattern of hexagons and pores (showing green here). Each pollen grain is about one fifth of a millimetre in diameter. Plant genera can often be identified by the distinctive pattern on their surface.

The outer surface of pollen is full of minute pits and chambers that contain proteins that allow a plant to recognise pollen of its own species when it lands on its stigma, and reject foreign pollen. It's these proteins that quite literally get up your nose, trigger an allergenic reaction and set you off sniffing and sneezing.

The outer casing (known as the exine) is made up of a polymer called sporopollenin, which is incredibly resistant to biodegradation - which is why palaeobotanists can recover ancient pollen samples from deep in peat bogs and lake beds and extract and identify pollen samples from plants that grew there tens of thousands of years ago. It's a branch of botany that has given some very useful insights into how plant species distributions have changed during periods of rapid climate change, like the one we are experiencing now: studying the past in this way gives an insight in what is likely to happen to plant species in the future.

Since the exine of pollen is so resilient, it passes through the gut of insects unharmed, although the pollen contents are digested. Yes, that little white speck on this bumblebee's tail is bee-poo, made up of empty exines of pollen that it has eaten. Many hoverflies feed almost exclusive on pollen, leaving little piles of hoverfly poo on leaves, and I know of at least one enterprising entomologist who has collected and analysed this, in order to study hoverfly's pollen diet.

During the Vietnam war Yellow Rain - yellow specks coating plants in the jungle - was believed to be the result of Communist chemical warfare. Subsequent anaysis showed that it was bee faeces, produced by vast swarms of bees that sometimes rose into the air and defecated in unison.

Orange-tip Butterflies - More Than Just a Colourful Set of Wings?

2010-05-24T17:15:00.000+01:00

This tiny orange rugby ball is the egg of an orange-tip butterfly Anthocharis cardamines, attached to the flower stalk (pedicel) of a hedge garlic Alliaria petiolata plant in my garden. The caterpillar that hatches will feed on the host plant's developing seed pod, so the caterpillar must hatch soon after the flower is pollinated.

At higher magnification it's possible to see the beautifully patterned egg case, which will be the first thing that the caterpillar will eat when it hatches, before moving on to consumer tender young seed pods.

Female orange-tip butterflies (male seen above with wings open and shut) only lay a single egg per infloresecence, typically on lady's smock Cardamine pratensis but also on hedge garlic A. petiolata or on sweet rocket Hesperis matrionalis, although egg laying has been recorded on 35 members of the cabbage family (Cruciferae). You can see a fine photo of an orange-tip egg on lady's smock over at Stuart Dunlop's Donegal Wildlife blog. If more that one egg is laid per inflorescence the caterpillars resort to cannibalism, but the female butterfly can detect a pheromone signal left by another that has already laid an egg and will avoid that plant, minimising the risk of this gruesome outcome - unless it rains, when the pheromone is washed off.

Back in 1997 research at Monk’s Wood National Nature Reserve established that the female butterflies that use lady’s smock as a larval food plant are extremely selective in their egg laying habits. They choose large flower heads in open, sunny locations. Choosing a flower head with a large number of buds ensures that there will be enough food (seed pods) for the hungry caterpillar.

Research in Durham University back in 1983 suggested that they also have quite a narrow window of opportunity for egg laying – if the eggs are laid when the inflorescence is too old the developing pods will be too tough for the larvae to eat by the time that they hatch. This can sometimes happen if bad weather delays egg laying, as the butterflies are only active in sunshine.

In my garden this delightful butterfly breeds on all three of the larval food plants - lady's smock, hedge garlic and sweet rocket - which have overlapping flowering periods that collectively span a period of about six weeks. Each plant has different pod development characteristics - hedge garlic, for example, has much larger, tougher, faster developing pods than lady's smock - so I wonder whether any member of the orange-tip population in my local colony can breed on all three - in which case they might need to adjust their egg laying habits to suit the individual host's pod development rates - or whether there are sub-populations that specialise on breeding on each of the different possible hosts. If the latter is the case, that would respresent the first step in subdivision of the population and of one species splitting into three .............. evolution in action...... or maybe they're not that discriminating. Something worth closer study though, I think. With that in mind, I'm planning to breed the butterflies on lady's smock and on sweet rocket, which represent the extremes of the range of flower timing, then see if the resulting butterflies exhibit a preference for laying eggs on either host plant when they hatch.

Sources:

S.P.Courtney and A.E.Duggan (1983) The population biology of the orange tip butterfly Anthocharis cardamines in Britain. Ecological Entomology 8, 271-281.

Dempster, J.P. (1997) The role of larval food resources and adult movement in the population dynamics of the orange-tip butterfly (Anthocharis cardamines). Oecologia 111 (4), 549-556.

So Much for Intelligent Design ....

2010-05-18T14:36:00.000+01:00

At first glance it might seem that the elaborate mechanism that dandelions Taraxacum officinale use for presenting pollen to visiting insects is a masterpiece of functional design. Look across the top of a dandelion flower with a magnifying glass and you can see a forest of stigmas, divided and curled back at the top of a long style covered in pollen. This is the last stage in a developmental process that begins in the flower bud ....

.... where at this stage the individual florets that make up the flower head (capitulum) are just on the point of flowering. From the bottom upwards in the photo above, first you can see the ovaries that contain the egg cells that will become the embryo in the seeds, then above them are the stamens, joined in a long yellow cylinder.....

... seen here in a single floret. Notice how at this stage the ring of feathery hairs (the pappus), that will carry the mature seed aloft on the breeze, is already well developed. This floret is one from the centre of the flower and has no petal, unlike those around the edge that have ray petals for advertisement ....

... like this one, where you can see the single petal attached. At this later stage of development the style has now elongated inside that cylinder of stamens, forcing its way upwards like a piston and sweeping out the pollen as it goes, then splitting at the tip to reveal the receptive stigma where pollen delivered by a visiting insect will germinate.

The outer surface of the style is covered in a forest of short hairs that help to sweep the pollen out of that cylinder of stamens. Pollen adheres to the outseide of the style until an insect arrives and collects it, at the same time cross-pollinating the stigma with the pollen from another that it arrived with.

But to the dandelions, all of this elaborate floral choreography is redundant - a waste of energy. At some point in their evolution they acquired a mutation that allows their ovules (above) to develop into seeds without any need for pollination, producing clonal, identical copies of the parent plant. It's a process called apomixis, that's also found in some other plants, including some bramble species. So in dandelions all that complex and energetically expensive floral development and the provision of pollen and nectar to attract pollinating insects, now serves no purpose - it's a legacy of an earlier stage in evolution, when dandelions did need to be cross pollinated. In some species of dandelion the pollination mechanism is still functional, but not in the apomitic common dandelion. Perhaps, at some point in the future, mutations will disable the pollen- and nectar-producing mechanisms in apomictic dandelions and they'll be able to shed the cost of producing these expensive resources for no purpose. For the moment, though, all that redundant pollen and nectar is a wonderful resource for bees in spring ....

Four-eyed Fly

2010-05-10T20:27:00.001+01:00

These remarkable eyes belong to a male St. Mark's fly Bibio marci - which has not one pair of compound eyes, but two. This is the black fly that dances just above the grass on spring days, dangling its long hind legs. You can find a picture of this behaviour on Nyctalus's Stand and Stare blog. These dancing males are on the lookout for females, which they approach from below, and the conjecture is that those long, fine hairs in between each individual compound eye lens (ommatidium) somehow help in the fly's detection of movement above and precise positioning when he grabs a female.

Remarkably, male and female St.Mark's flies have quite different eyes and are also distinctive in other respects. In this mating pair the larger female is above, with the more slender head, heavier body and smokey-coloured wings.

Both sexes have one pair of exceptionally long legs, that dangle below in flight, although the extent of the difference in leg length is over-emphasised in this picture of a male because the front two pairs of legs have curled up in death.

This head-on view of the male reveals a distinctive horizontal groove across each eye, just below the mid-point. In fact upper and lower eyes are quite separate on each side and have separate connections to the brain, where the images they produce are processed separately - the upper eye on the look out for females, the lower monitoring ground position. This fly has four eyes (as do whirligig beetles which swim on the surface of ponds and simultaneous look towards the sky and down into the water).

The female's heavier body, smokey wings and narrow head are evident in this side view, while ....

... a close-up view of the female's head reveals that her eyes are smaller and hairless - but then she doesn't have to worry about finding males; they find her with their strange two-tier visual system.

Orchid Roots: Botanical Sponges

2010-05-06T19:00:00.000+01:00

You can crudely divide orchids into two groups: ground orchids, rooted in the soil - like Pleione species, for example - and epiphytic orchids like the one below, that often grow on the branches of trees in tropical forests. The dangling roots of the epiphytic types have a dual role, sometimes anchoring the plant and always acting as storage vessels for water that they absorb from mist and sudden tropical downpours. If you cut a section through one of these roots (above) you can see their unique structure, that allows them to absorb and store water. The bright yellow ring of thick-walled cells at the bottom of the image above is the plant's internal plumbing - the pipes (xylem vessels) that conduct water from the roots to the leaves and flowers. Beyond that the thin-walled blue cells are the packing cells that are alive and contain some chloroplasts, like the leaves. Beyond that, sheathing the root and separated by a distinct layer of mostly hexagonal cells is an outer sheath of dead cells called the velamen layer, and their role is to soak up water as the roots dangle in the air, high above the forest floor. They are, in effect, a sponge.

The recommended way to water tropical orchids, like Vanda species for example, is simply to stand them in water for a few minutes each day, so their root velamen layer fills up with water, then simply hang the plants up with their roots dangling in space.

You can see here what happens when you water an orchid root here. When it's dry (above) the dead velamen layer cells reflect light and the whole root looks silvery-white. Make them wet for just a few seconds (below) and those dead cells fill up with water, become translucent and reveal the green photosynthetic tissue within.

Potatoes: the Inside Story

2010-04-13T19:01:00.000+01:00

These beautiful objects are potato starch grains. Slice a potato, shake the slices in a glass of water and the water will become milky due to the release of starch from the broken cells. Put a drop of this milky water on a microscope slide, viewed it under a microscope using polarised light and this is what you see. The starch itself is colourless and translucent - polarised light is responsible to generating the colours and the distinctive ‘Maltese Cross’ pattern in the grains. Starch grains are polymers of glucose molecules and are the means by which plants store energy for future use. It is breakdown of starch in stems, roots, rhizomes, buds and leaves that is - as this very moment – releasing the energy that plants are using for new spring growth, before photosynthesis in their leaves takes over the job. It’s also starch that provides most of the calorie intake for almost all of the human population on the planet.

The form and size of starch grains varies depending on plant species and in potato they are relatively large – up to one tenth of a millimetre in diameter. Very fine starch, such as that produced in the tubers of cuckoo pint was used to stiffen cloth and was used by the Eliabethan courtiers to stiffen their magnificent ruffs.

Botanical Flypaper

2010-03-31T17:25:00.002+01:00

The tiny insect in the photo above, just a couple of millimetres long, is doomed. Its body and wings are held fast by the sticky leaf hairs of.....

.... this plant, a butterwort Pinguicula moranensis that originates from Guatemala and Mexico. Like all butterworts, it captures small insects on its leaf surface and then, when they die of exhaustion, slowly digests them.

Almost the whole of the plant surface is covered with these minute stalked hairs, of varying heights for maximum trapping efficiency,each tipped with a droplet of sticky mucilage.

Seen here at higher magnification and in side view, each bottle-shaped hair is composed of a single cell rising from one of the surface epidermal cells, topped with a glandular cap that at higher magnification still...

... is revealed to be made up of eight separate secretory cells, each shaped like a slice of cake, perched on the top of the stalk. Meanwhile, down below and embedded in the leaf surface.......

... there's a different kind of gland, seen here in surface view amongst the jigsaw puzzle-shaped epidermal cells of the leaf. Each leaf upper surface is studded with hundreds of these glands. Once and insect is trapped the glands nearby........

..... like this one, seen here in side view at higher magnification, secrete digestive enzymes. When the insect finally dies....

... it collapses into the pool of digestive enzymes and is slowly dissolved, until only its outer chitin exoskeleton remains, like a ghost of the plant's victim. Then the plant absorbs the resultant 'soup', rich in the essential nitrogen that's lacking in this carnivorous plant's boggy habitat. However, not all insects succumb so easily. The plants in my conservatory almost always host...

... small colonies of to these tiny aphids. Even though they are held fast, they can still use their piecing mouthparts to puncture the plant's cells and feed, and survive long enough to produce the next generation of young, which are born by virgin birth (parthenogenesis) without the need for mating. If you double-click on this image for a larger view you'll see a pair of minute claws at the tip of each aphid leg. On most host plants these would allow the aphid to grip the plant surface and walk, but the epidermal cells of butterwort are so smooth and slippery that the claws cannot grip. If you watch under a microscope, you can see the claws simply sliding over the plant surface, so the anchored aphid can do nothing other than feed and breed before it eventually dies, leaving a ghostly shell and a clone of itself behind.

Butterworts' flypaper-like properties make them very useful plants to grow if you are troubled by the tiny mushroom flies that emerge from potting composts - a single plant will trap and kill scores of them.

Grey Killer

2010-03-28T21:22:00.000+01:00

Spring is a rollercoaster ride of hope and despair for gardeners, as tender new seedlings run the gauntlet of frosts, pests and diseases. This fungus, grey mould Botrytis cinerea, is one of the worst killers of plants grown in poorly ventilated, cold clammy greenhouses. Initially, it usually colonies dead or damaged plant tissue like last season's leaves or stems ....

... producing a furry coating for spore clusters on short aerial hyphae.

The fungus can produce these clusters of spores, known as conidiospores, in vast numbers, and at higher magnification you can see...

... that each hyphae is branched at the tip. You can also see the cross-walls in the hyphae that indicate that this is an ascomycete fungus

At high magnification the tip of the hypha can be seen to branch, with clusters of spores at the end of every branch....

... that are dispersed on the breeze as a grey cloud when infected plants are disturbed. Grey mould is a major killer of plants but paradoxically it does have its uses. Grapes that are infected with 'noble rot' - as the fungus is known in viticultural circles, produce a much more intense flavour, as the fungus withdraws water from the grape and concentrates the flavour..... a property that's exploited in the production of sauternes dessert wine.

Anticlockwise tubeworms

2010-03-21T20:20:00.001Z

The calcareous spiral tubes of tubeworms, attached to wracks and kelps that are washed up on the strandline, are a common sight on the seashore. There are several different species and the first step to identification is to see whether the tube coils clockwise or anticlockwise. If it's clockwise, then it'll be a species of Spirorbis but if it's anticlockwise, like these, and the tube has three distinct ridges, then it's a worm called Janua pagenstecheri. The coiled tube is about 2mm. in diameter.

If you watch the live worm under the microscope it soon everts its crown of transparent feeding tentacles. If you look just to the right of the tentacles you can see a brown, translucent flap. This has a dual function, closing off the tube when the worm withdraws its tentacles and acting as a brood chamber for the worm's embryos. The pink encrustation in front of the worm is a alga, not part of the animal.

Fungal Artillary

2010-03-16T20:11:00.000Z

Most fungi tend to be associated with autumn but there are a number of perennial species that can be found at any time of year, including this one - variously known as King Alfred's cakes, cramp balls or Daldinia concentrica. The first name refers to King Alfred's culinary accident while hiding from marauding Danes in the humble abode of a cowherd; the second refers to the folklore that carrying this fungus around in your pocket stops you getting cramp in the legs (doesn't work for me); the last refers to .....

.... the concentric rings of annual growth that you can see if you cut the fungus open.

The blackened surface of the fungus is covered with scores of these 'pimples', each with a pore in the centre. Each leads to a chamber below, packed with tubular flask-shaped fungal hyphae called asci, each with eight ascospores inside. Cut one of these chambers (in mycological parlance a perithecium) open and this....

... is what you see under the microscope - rows or rugby-ball shaped spores, seen here at around x100 magnification and ....

.... here at x400 magnification. In spring each ascus of eight ascospores elongates in turn, until its tip protrudes from the pore in one of those surface 'pimples', like a cannon protruding from the gun port of a man 'o war. Pressure builds inside the ascus until it ruptures and fires out its salvo of spores. Then it withers, another elongates to take its place and the discharge is repeated. This can go on for 6-7 weeks before all the asci have fired their broadsides, with most of the spore discharge taking place at night. You can watch this by placing the fungus in a light beam in a warm room - if you've got sharp eyes you can see what look like little puffs of smoke all over the surface - the fungus firing its silent broadsides. In England Daldinia concentrica mostly grows on ash trees but in Scotland it also grows on birch.

Another Living Jewel

2010-03-07T20:47:00.000Z

My last post showed a jewel-like case made by a single-celled amoeba. This one shows the remarkable case made by a marine worm. We found this little tapered tube, about 5 cm. long, on the sandy beach at Warkworth in Northumberland this afternoon. It was made by a worm called Pectinaria koreni and when the animal inside is alive only the last few millimetres of the narrow end of the tube protrudes above the sand. The worm lives head-down in the sand, drawing in a current of water through the narrow end of the tube.

You can see the dark zone at the narrow end here - that's the bit that normally protrudes above the sand. The tube is made up of hundreds of sand grains and minute shell fragments, selected for smoothness inside and outside the tube and ....

.... neatly fitted together with a degree of precision that a stonemason would envy....

.... and although the tube is only one sand grain thick it's remarkably strong. That's because....

... the worm secretes a form of cement that glues the grains together, like mortar in a wall ......

.... as you can see here at higher magnification.

A pair would make rather fine ear-rings, provided the wearer didn't have any qualms about wearing jewellery made by a worm rather than by a jeweller.

You can see a picture of the worm here.

A Living Jewel

2010-02-22T20:41:00.001Z

This exquisite object, nature's equivalent of a Fabergé egg but only about one tenth of a millimetre long, is a testate rhizopod - a species of amoeba that lives inside a balloon-shaped shell. Testate rhizopods either secrete their shells or they cement minute sand grains together to create one. When you think about it, that's a remarkable feat of construction for one of the lowest forms of life that, superficially, is little more than a slithering blob of cytoplasm. You can see some more examples here. Testate rhizopds that assemble a shell from sand grains are often assigned to the genus Difflugia and scores of 'species' have been described, based on the components and construction of their shell, although it's not clear to what extent these are really distinct 'species'. You can download a guide to identification and where to find them here. I found this specimen when I was screening a sample of water from amongst the waterweeds on the edge of a pond in Durham. I have to admit that the image above has involved a bit of optical trickery because.........

... this is what I saw when I first examined the organism under normal bright field microscopy, revealing the translucent quartz grains that formed its case. Switching to dark field microscopy....

... where the image is formed from light diffracted by the translucent grains showed them in a new light. But it was only when I switched to polarised light microscopy, which reveals the interference colours formed by the birefringent grains, that the ultimate beauty of this tiny organism's case was revealed.

Jewellery on a microscopic scale...

Cyclops with Hitch-hikers

2010-02-17T22:22:00.001Z

This little crustacean, about a millimetre long, is Cyclops, with a single red eye-spot in the centre of its head - a minute freshwater counterpart of the monocular monster of Greek mythology. My garden pond is swarming with them at present, even though the ice has barely thawed. If you take a close look at the top end of the tail, near the body, you can just make out clusters of short-stalked objects attached to the animal's exoskeleton. At higher magnification these turn out to be....

.......... Vorticellids - single celled protists with beating cilia around their mouth, creating a whirlpool current that sucks in foot particles. You can see a movie of Vorticella in action here. At even higher magnification..........

..you can see their cilia and the contractile vacuoles that they use to expel waste (double-click for a larger image). Vorticellids attach themselves to all sorts of small pond animals, hitching a ride.

As Jonathan Swift (1677-1745) noted,

So, naturalists observe, a flea

Has smaller fleas that on him prey;

And these have smaller still to bite ’em;

And so proceed ad infinitum.

Knapweed nemesis...

2010-01-31T19:13:00.002Z

This little barrel-shaped grub is the larval stage of a picture-winged fly Urophora jaceana, which spends the winter hidden deep inside the seed head of a knapweed plant. Late last summer the adult female fly would have....

...laid its eggs in a knapweed flower like this and since then the larvae have been feeding on the developing seeds inside. The larvae induce the formation of a hard, woody gall inside the seedhead so if you.....

... gently squeeze a seed head like this one you'll find some that are squashy and some that have a hard lump inside, which is the Urophora gall. If you carefully cut the gall open ...

.. the larvae are revealed in their chamber inside. Here, a fully-fed larva is on the right and one that has developed into a pupa is on the left.

By this stage most of the seeds (on the right here) have usually been eaten but sometimes you'll find a few survivors.

This pupa will hatch out early this summer, just in time to lay eggs in a new crop of knapweed flower buds.

European knapweed species were taken to North America and have since become noxious weeds there. In an attempt to control them Urophora species, which can have a major impact on the plants' reproductive capacity, were introduced too as a biological control agent. The gall fly hasn't halted the spread of the knapweed but it has provided a nourishing food supply for North American deer mice in winter, to the extent that in Montana there has been a population explosion of well-fed deer mice. When the ground is covered in snow they climb the knapweed stalks and eat the Urophora grubs. The sudden population increase is causing some concern since they carry hantavirus, which is present in their urine and can be transmitted to humans - an unexpected consequence of a chain of events that started with Europeans carrying knapweed to the United States. It's also another example of how biological control techniques can have broader consequences than intended by those who introduced the biological control agents. Curiously, I don't think our local native field mice in Britain have yet discovered that there's a rich source of animal protein in the gall-fly infested knapweed seed heads - after the recent heavy snowfalls I couldn't find any evidence of field mice having foraged on knapweed seed heads around here. Maybe deer mice are just a bit smarter...........

Nature's Pole-vaulter

2010-01-26T20:35:00.002Z

This engaging little animal is a springtail – a member of an ancient lineage of six-legged arthropods called the Collembola, that resemble insects but differ in having internal rather than external mouthparts. Springtails are everywhere and most live on detritus. This one, which was about half a millimetre long and just visible to the naked eye - and which I think belongs to a genus called Deuterosminthurus - was rambling over the surface of the soil in a flower pot in our conservatory. Lift up the lid of your compost bin and you’ll often see swarms of them scuttling around on the surface ........ and if you disturb them they leap into the air, using.......

... a specialised structure called a furcula attached to their tail and folded underneath the springtail. You can just see it in this photo, behind the set of legs closest to the camera, pointing towards the head. Springtails use their furcula much in the same way as a pole-vaulter uses their pole. It’s under permanent tension and when the animal releases it from the catch that holds it in place it flicks down instantaneously, catapaulting the animal into the air and away from danger. The tip of the furcula in this species is .....

forked – as you can see here, where it appears to be using it to scratch its mouth.

While I watched this particular animal gave itself a pedicure and rather remarkably you can see that it’s got all three legs on one side off the ground.... so why doesn’t it fall over? If your dog did that, lifting both legs on the same side, it would roll over.... but maybe if it had six-legs instead of four it wouldn't because.....

...... as you can see when the springtail tilted itself the other way and lifted all three left-hand legs off the ground, the right hand legs are acting like a tripod with feet evenly spaced at the points of a triangle.

There are numerous species of springtails that are fascinating to study, if you have a microscope. You can find a wonderful photoguide to many of the species in Britain here and you can see a wonderful movie, from David Attenborough's Life in the Undergrowth at http://www.youtube.com/watch?v=OwOL-MHcQ1w showing these pole-vaulters in action.

Some like it hot: the Firebrat Thermobia domestica

2010-01-19T07:40:00.001Z

One of the pleasures of being a professional biologist is that people often bring things for me to identify that I might otherwise never see. This strange insect – a firebrat Thermobia domestica – arrived today in a jam jar. It was a little tattered – with a couple of broken tail spines and a damaged antenna, but still very much alive.

Firebrats are relatives of the much more familiar silverfish – primitive wingless insects belonging to an order known as the thysanura and commonly known as bristle-tails. One of their most curious features is that they’re totally covered with overlapping, iridescent scales rather like the scales on a butterfly’s wing.

Unlike silverfish, which tend to live in damp places like the space under baths and cupboards under stairs, firebrats can only survive in warm places and are very drought tolerant. They thrive at temperatures of around 37C and were once common inhabitants of crevices around bread ovens in bakeries. The name firebrat refers to the fact that crevices around hearths of open fires also suited then very well.

Thysanura, the name of the order to which bristletails belong, is derived from two Greek words meaning ‘fringed tail’ and you can see here the fringes on the central tail filament and its two flanking cerci. A large specimen is about a centimetre long, including the tail filament.

As soon as the insect was placed under the warm light of a microscope it perked up and demonstrated its ability to move like greased lightning. I’d rather like to get hold of a few more specimens, because I came across this fascinating description of their courtship in a book called The Living House by George Ordish, published back in 1960. “Firebrats have a curious courtship procedure”, he writes, ”not unlike that of the display of birds. The male dances in circles around the female and repeatedly touches her with his antennae. The actual mating is somewhat akin to that of spiders in that the male deposits a sperm bag in front of the female and then retires, while the female herself undertakes the necessary movements to absorb it, if she so desires”.

The Hidden Secrets of Ferns

2010-01-08T22:56:00.003Z

Fern spores are produced in vast numbers on the understide of fern fronds during the summer months. For details of how they are catapaulted into the airstream, take a look at http://beyondthehumaneye.blogspot.com/2009/07/natures-siege-catapults.html

Each spore is less than a hundredth of a millimetre in diameter and can be carried vast distances on air currents. Ferns are often the first plants to colonise bare volcanic lava flows, carried there as spores on the wind.

All they need for germination is water and mineral salts. They swell, the brown spore case splits open and a hair-like rhizoid emerges, that anchors the spore to its substrate. Then a green photosynthetic cell emerges from the spore.

The photosynthetic cell divides longitudinally, forming the beginnings of a short chain of cells. The green blobs in the cells are chloroplasts.

The chain of cells continues to elongate until it reaches 6-7 cells long, dividing longitudinally and producing more rhizoids to anchor itself more firmly. At this stage the remains of the brown spore coat is still visible. During this stage of development the plant must be constantly wet - even a short period of drought will be fatal. I sowed these spores in September, so they've taken about four months to reach this stage, where they appear to the naked eye as a green film covering wet soil.

This is the next crucial stage in development and is about a millimetre long. The tip cell of the thread now begins to divide laterally and longitudinally, forming a flat plate of cells ....

... here you can see this two-dimensional tip division at higher magnification. The flat plate of cells that develops from this is known as the prothallus, and this is where fern sexual reproduction takes place..

These are two fully developed prothalli, each about 5mm. in diameter and only one cell thick. They are incredibly delicate and must remain permanently wet to survive. At this stage they are about six months old and male and female reproductive cells form on their surface.

These are the male antherozoids, enclosed in a structure called the antheridium. When this bursts the antherozoids are released in swarms and swim, propelled by lashing flagellae, like tiny spinning tops in the surface film of water, in search of a female egg cell inside a long-necked structure called an archegonium, which you can see here. After a successful fertilisation an embryo deveops which ultimately grows into a .......

.......new miniature fern plant. In the early stages, as seen here, it's still attached to the prothallus formed by the germinated spore but that soon withers away and the new fern grows by producing a series of ever-larger fronds. It usually takes about a year after sowing to reach this stage.

Provided you have the required patience, ferns are not difficult to grow from spores. For detailed instructions, visit http://website.lineone.net/~margaret_cole/SFG7/growing%20ferns.htm

For more on the fascinating world of ferns, visit http://www.nhm.ac.uk/hosted_sites/bps/

High-density Housing (for Bryozoans)

2009-12-27T10:21:00.001Z

This beautifully geometric piece of natural architecture is produced by the animal commonly called the sea-mat and scientifically known as a bryozoan (which means 'moss-animal'). This particular species is Membranipora membranacea and I picked it up yesterday, in a rock-pool on the seashore at Seaburn, near Sunderland.

Membranipora forms extensive, fast-growing colonies resembling a lacy mat, that spread over the surface of kelp fronds. It's common on all coasts around Britain and has been introduced into shallow seas in other parts of the world where there is some concern that its rapid rate of growth could suppress the reproduction of some marine algae.

Each calcareous compartment, secreted by the animal inside, contains an individual animal (zooid) that extends a feeding arm called a lophophore, for filtering out plankton.

The zooids retract into a tube within their walled enclosure at the slighest hint of danger but when they're all extended they resemble a garden of transparent flowers, gently waving their arms..

Each walled enclosure has a small tower at the junction with its neighbours' walls and ......

....there are often gaps in the walls, which give the colony a degree of flexibility as the supporting kelp frond bends in the sea currents. The gaps tend to be most conspicuous in older sections of the colony.

There are at least two kinds of zooid - the flower-shaped feeding lophophores and these translucent cylindrical forms.

I'm not sure what their function is but my guess is that they provide additional surface area for oxygen uptake or maybe waste disposal.

You can find out more about bryozoans here or take a look for yourself - these are low-power micrographs (maximum magnification x50) but you can see the living zooids with a hand lens if you put a piece of the colony in a shallow dish of seawater. You can find them all year-round and fine specimens are often attached to kelps that are washed up on beaches after storms.

The Ultimate Solar Cells

2009-12-07T22:33:00.001Z

These green blobs are chloroplasts - in this instance packed inside the cells of a moss leaf and magnified around 400 times - upon which our collective future depends. Using only energy from sunlight, water and carbon dioxide from the atmosphere, they produce the oxygen we breathe, control the climate by removing carbon dioxide from the atmosphere and, directly or indirectly via plants and animals, produce all the food we eat. Currently 6.3 billion of us depend on them for our survival. By 2050 9 billion of us will need their services. Maximum respect for plants, then..... and, more precisely (see Psi Wavefunction's comment), chlorophyll, in all of its manefestations, wherever it occurs