Four-eyed Fly

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

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

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

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

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

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

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

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

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

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.