Friday, July 31, 2009

Bird Bath Voyager

This little organism, about a tenth of a millimetre in diameter, is an alga called Stephanosphaera pluvialis. It’s almost always found in bird baths and this one came from the gutter around our conservatory roof , which is always full of water and is regularly used for bathing by the birds in our garden. Stephenosphaera consists of eight photosynthetic cells, each with two lashing flagellae, encased in a gelatinous sphere that’s a clear as glass. Driven by the flagellae, the whole organism rolls through the water (see rather shaky video clips) - eight tiny cells in their gelatinous survival capsule, on an endless journey through the oceans of our conservatory gutter. It's carried from place to place on the feet and plumage of birds.

Saturday, July 25, 2009

Butterfly Eggs Hatching

This small white butterfly Pieris rapae took about twenty minutes to lay its cluster of eggs on the underside of some broccoli leaves in our garden. Each egg as laid with slow painstaking precision, at the rate of roughly one every twenty seconds. After laying each egg the butterfly withdrew its abdomen back between its wings, then bent it downwards and deposited another. Butterfly eggs have beautifully sculptured chitinous shells and as hatching nears they become more transparent, so that you can see the larva wriggling inside. After hatching, the caterpillar’s first act is to each its own egg.

Friday, July 24, 2009

Oak Leaves Under Attack

Several tree species - most notably oaks - put on a new flush of growth in summer, sending out shoots with fresh green foliage (bottom photograph) to supplement the older leaves of spring that have suffered from insect attack and general wear-and-tear. The new shoots are known as Lammas growth, because they’re well developed by the ancient Celtic harvest festival of Lammas day - 1st. August. Lammas growth is most prominent in younger trees during this 'second spring', but sometimes the freshness of this new foliage doesn’t last very long. Take a look at the new shoots and you’ll find that many will be distorted and coated with a greyish-white powder (second photo from bottom). This is the parasitic oak powdery mildew Erysiphe alphitoides that thrives in the warm, humid weather that we’ve been experiencing lately. Under the microscope you can see a mass of transparent fungal hyphae covering the leaf surface (third image from bottom) visible in the microscope photo (x400) in the clear areas between the blocks of green tissue. The hyphae draw their nutrition from the delicate new leaf tissue and send up short aerial hyphae that bud-off powdery spores (fourth and top images, x100 and x400 respectively), that blow away in the wind and infect another leaf.

Thursday, July 23, 2009

More Grey Hairs

I seem to be acquiring more grey hairs with every passing day at the moment, so I thought I might as well take a look at them under the microscope. Magnfied x400, it's clear that the grey ones aren't so much grey as colourless (foreground) - increasing numbers of my hair follicles have given up making melanin pigment.

Tuesday, July 21, 2009

Flatworms:Minute Predators of the Rock Pool

One of the easiest ways to find the smallest animals that inhabit rock pools at the seaside is to collect fronds of red seaweed and examine them in a shallow dish of sea water under a low power microscope. I discovered this little flatworm this afternoon amongst the seaweed fronds from a rock pool on the Northumberland coast at Low Newton. It’s about two millimetres long and the images here were taken at magnifications of x40 (whole animal), x100 (head) and x400 (eye). Free-living flatworms, some tropical examples of which are over 30cm. long, belong to a very large phylum of animals called the Platyhelminthes that includes notorious parasites like liver flukes. These minute marine flatworms are predators on even smaller marine organisms. Their mouth is in the middle of the underside of the flattened body and opens into a highly branched digestive tract that you can see clearly as the dark brown network in the low power image of the whole animal (top). Flatworms are equipped with a pair of very simple eyes that are efficient at detecting the direction of light but don’t form images. They open via a ‘pinhole’ (just visible in the bottom photograph) and are lined with just a few light receptors attached to nerve endings. Flatworms glide around with the aid of thousands of rhythmically-beating cilia (see video) that cover a surface layer of large brick-like cells that you can see around the edge of the animal in the middle photograph. Freshwater flatworms that are very similar to this marine species, but are black rather than translucent, are present in every garden pond and can often be seen gliding around under the surface film.

Friday, July 17, 2009

Fragrant Foliage

If you’ve ever brushed against a scented-leaved Pelargonium like the one above (or any other fragrant-leaved plant) and noticed the scent, here’s where that fragrance is actually stored. The leaves are covered in fine pointed hairs (second photo from bottom) but scattered amongst them there are two other kinds of hair – short (third from bottom) and tall (fourth photo from bottom). At higher magnification (top photo) you can see the oily fragrance compounds stored in the bulbous cell at the tip of the hairs, that are released when the hairs are damaged. These fragrance chemicals are a key part of the plant’s defence system against insects and are secretions that either make the leaf too sticky for small insects to move around or repel them, but commercially they are of immense importance in the fragrance industry. Many of those scents that saturate the air around the perfume counter in department stores contained chemical compounds distilled from the ‘gunk’ that you can see in these plant hair tips. Perhaps the most extraordinary is labdanum, which is stored in the sticky hairs of Cretan rock roses (Cistus species). Tradionally, this was once collected by scraping it off the fur of goats that grazed amongst the Cistus shrubs on Cretan hillsides. You can read about it at

Wednesday, July 15, 2009

Nature’s Siege Catapults

Turn over a fern frond at this time of year and you’ll find that the underside is covered in rows of what look like small blisters (bottom photo). These are scores of spore- producing structures called sporangia, clustered together under a membrane that keeps them moist while they’re developing. In the example illustrated here the membrane is kidney-shaped, which is characteristic of a buckler ferns in the genus Dryopteris. Once the spores in the sporangia are ripe the protective membrane withers and at this stage the sporangia – sometimes more than a hundred in each cluster – look like minute black eggs when you look at them with a hand lens (second and third pictures from bottom - double-click any image for an enlarged view). Each individual sporangium is a minute catapult that fires its spores out into the airstream. You need to look at a sporangium under a microscope to see its detailed structure and decipher how it works (top photo). Each sporangium, mounted in a stalk and stuffed full of spores, is egg-shaped and has a 'spinal column' of thick-walled cells (showing up in vivid colours in these polarised light micrographs) stretching about two thirds of the way around its vertical circumference. Once these cells are exposed to air they lose water through their thin outer wall that you can see in the second photograph from the top, drawing this outer wall inwards via the surface tension of the remaining water inside. This creates tension inside each cell and, repeated all the way along that ‘spinal column’ of cells, draws the 'spinal column' back like a bowstring, ripping open the sporangium and exposing the spores inside. Eventually the remaining water in each cell in the 'spinal colum', under immense surface tension, vapourises instantaneously and the natural springiness of the thick walls of the sporangium flicks the spine back to its original position, hurling out the spores like rocks from a Roman siege catapult. Once the spores - each around a hundredth of a millimetre in diameter - reach the airstream they can be carried vast distances. Ferns are often amongst the first plants to establish themselves on new volcanic islands and lava flows, thanks to their spores' incredible aerial mobility, which also allows them to colonise unlikely places in urban environments. Next time you're walking through any city, look up at the gutters and you'll see ferns growing that arrived as wind-blown spores. What happens next, after a spore lands and germinates, is an equally remarkable tale of frantic sexual reproduction .... but that’s another story.

Tuesday, July 7, 2009

Seed sculpturing

Fruits and seeds are often aesthetically pleasing natural objects but they reveal a whole new layer of complexity under the microscope. This is the ripe seed capsule of red campion Silene dioica which has just split open at the tip, with the segments at the apex rolling back to form a ring of teeth. Inside are the seeds, each bearing a complex surface pattern on their seed coats. Fruit and seed structures are often doagnistic characters within plant families and many species in the campion family (Caryophyllaceae) have capsules like this that split open to form a ring of teeth, that open and close depending on air moisture levels, protecting the seeds during wet weeather and opening to allow them to be shaken out when the sun shines. You can see another example at