Sunday, May 31, 2009

Cuckoo Spit

All the goosegrass under the hedge outside my garden is covered with frothy bubbles of cuckoo spit – and here’s one of the perpetrators, the nymph of a frog-hopper Philaenus spumarius. Adult frog-hoppers, or as they’re known in the US, spittlebugs, ping around the vegetation like little grasshoppers, plugging their feeding tube into plant stems and siphoning off sugar, but the nymph goes one stage further, feeding on the sugar and blowing itself a coccoon of bubbles to keep itself moist while it completes its development, eventually becoming enclosed in a hard, waterproof covering that allows it to live outside of its bubblebath. Adult frog-hoppers have very variable colour paterns – you can see some of them at

Thursday, May 28, 2009

Taking the Pith

Even as a dyed-in-the-wool botanist I have to admit that rushes (Juncus species) are pretty dull plants – just spiky bunches of cylindrical leaves growing in mud around pond margins (bottom picture) or dominating large areas of poorly drained upland pastures. But, as the old saying goes, ‘beauty is more than skin deep’ and to find the really attractive feature of this plant you have to delve below the leaf surface. Peeling back the outer layer of green photosynthetic tissue reveals a cylinder of spongy pith, as light as thistledown. Pith peeled from rushes and dipped in tallow was once used to form the wicks of rush-lights, a smoky-flamed form of interior lighting that was eventually replaced by gas mantles and then electric light. Take a look at these pith cells under the microscope, in a cross-section of the cylindrical leaf (see top picture) and their real beauty emerges. The individual cells, shaped like starfish, form three-dimensional interior scaffolding for the cylindrical leaf. Each ‘starfish-cell’ is joined to its neighbours by the tips of its arms, forming a three-dimensional lattice (see second picture from top). The top two photomicrographs were taken using fluorescence microscopy, where the section of the leaf was treated with a compound (in this case auramine) which fluoresces when illuminated with blue light, giving an very attractive green glow that shows the three dimensional structure of the plant tissue particularly well. Double-click the top image for a better view. To find out more about rush lights, visit

Monday, May 25, 2009

Testate Rhizopods

Amoeba come in a wide variety of shapes and sizes. The bog-standard, free-range amoeba glides wherever its pseudopodia take it, going with the flow of its protoplasm (see movie). Heliozoans – amoeba with spines (see earlier post) – roll trough the water. A third form, testate rhizopods pictured here, secrete a glassy shell for themselves, that reminds me of a hot-air balloon or a Greek amphora, and send their pseudopodium ('false feet') out from the opening to engulf anything that’s smaller than themslves and within reach. The upper testate rhizopod here is alive, with an amoeba inside the shell. The yellowish objects within are partially digested small algae or diatoms that it’s grabbed. The image below is of an empty testa, this one with spines and showing the surface patterning on its glassy surface. Different species can be recognised by their testa pattern. They are both about one tenth of a millimetre long and were photographed with a simple microscope, without any fancy optical tricks. They came from a boggy spring in Teesdale.


Sunday, May 24, 2009

Hairy Stomachs

TV wildlife documentaries tend to focus on large animals with fur or feathers, but most of the animal world is tiny and many of the microscopic life forms that live in the water or in soil, that play a vital role in the functioning of ecosystems, are poorly understood. This animal is a gastrotrich – a name that literally means ‘hairy stomach’, on account of the tiny beating hairs on its underside that propel it through the water. These restless little animals, none longer than half a millimetre, are in every pond and also occur in marine environments, but compared with larger life forms we know very little about the lives of the 400 or so species that have been discovered so far. If you have a garden pond, or any water in the garden that contains decaying vegetation, there’ll be gastrotrichs in it, along with the heliozoans and rotifers that I mentioned in earlier postings. Gastrotrichs are fast moving, endlessly exploring detritus in the water in search of a meal, and defend themselves with tiny spines on the body surface. I used DIC optics again for these pictures, to highlight the animal’s spiny covering.

Saturday, May 23, 2009

Porcupines of the Pond

This amazing creature is a heliozoan (literally ‘sun animal’), which is an amoeba that surrounds itself with a formidable battery of needle-sharp spines, radiating out from its core like sunbeams. Heliozoans are between a tenth and a quarter of a millimetre in diameter and drift through the water, slowly spinning. Each spine has a thin film of cytoplasm that flows up to its tip and them back down into the core, and any small food particles that the tip of the spine contacts are carried downwards on this conveyor and engulfed into the food vacuoles of the organism. The size of the core varies – normally it’s quite compact but it can expand by forming a mass of vacuoles (second and third photos down) and if it’s seriously stressed, like the heliozoan in the bottom picture, it flattens its spines and crawls across surfaces like a normal amoeba. These specimens came from water squeezed from moss on the edge of a pond. I used a microscope equipped with differential interference contract (DIC) optics to show the internal structure and needle-like spines. DIC optics generate a three dimensional image of transparent objects, which are otherwise difficult to see with conventional microscope optics.

Friday, May 22, 2009

Getting a Grip

The colour of a flower is the result of a combination of the floral pigments contained in the petal cells and the optical characteristics of the cells themselves, which is why the colour of flowers in photographs doesn’t always correspond exactly with what the eye sees. The cells walls act like lenses, bending and scattering light rays, producing optical effects that combine with the floral pigment colours to produce unique hues, so even a brick red geranium flower shows a bluish tinge from certain angles (bottom picture). These photos show the cells on the surface of a geranium (Pelargonium) petal, which in surface view look like a patchwork blanket, with the patches stitched together (second picture from bottom x100). A side-on view reveals that each cell is actually shaped like a small hill, and that the ‘stitches’ are really pleats (third picture from bottom x100 and fourth picture from bottom x200). The conical cells are typical of many petal surfaces of flowers visited by insects. So why are they this shape? Their lens-like properties contribute to flower colours but their shape and surface texture seems to have evolved to give the claws of pollinating insects like bees (top picture x100) something to grip. By the clever use of mutant forms of snapdragon that have flat, smooth petal surface cells rather than conical ones, Dr. Beverley Glover at Cambridge University’s Department of Plant Sciences has shown that bees avoid smooth petal surfaces because it’s difficult for their claws to grip them and gain enough purchase to force their tongues into the flower. So ultimately it’s the necessity of giving insects a foothold that has produced petal cells with optical properties that add complexity and subtlety to flower colours. There's more about Dr. Glover's research in this web site

Wednesday, May 20, 2009

Animated Cotton Wool

Turn over an alder leaf at this time of year and you may find what look like small lumps of cotton wool stuck to the leaf blade and leaf stalk. Watch for a while and they move around. They’re insects – the nymphal stage of alder psyllids Psylla alni, which feed on the sap of the plant. The source of the ‘cotton wool’, which is really a mass of waxy filaments secreted by the insect, becomes apparent when these aphid-sized insects are examined under the microscope. The wax is produced by glands at the tail, so a psyllid that’s just begun to produce this material looks like its tail is on fire. The wax is a defence against water loss and predators. The nymphs have stubby wing primordia that eventually develop into fully-formed wings, by which time they will have shed their ‘cotton wool’ covering, ready to take flight and disperse. Psyllids are commonly known as jumping plant lice and different species tend to be associated with specific plant hosts. The alder psyllid is one of the larger species in the UK.

Monday, May 18, 2009

Every Fly’s Nightmare

I found about a dozen dead flies like this one, head down, tongues extended, clinging to the flower heads of meadow foxtail grass. They’ve been killed by a fungus called Entomophthora muscae, that invades the insect through one of the joints in its external skeleton and attacks its nervous system, modifying its behaviour so that it climbs to the top of grass stems and clings on while the fungus digests its internal organs. Fully fed, the fungus then erupts through the joints in its victim's body, covering the dead fly's abdomen with a felty mass of fungal material that produces gelatinous-coated spores that cling to the next hapless fly that arrives in the scene, sealing its fate. The spores can be fired some distance from the corpse, so they also coat surrounding vegetation. The bottom photograph shows the highly magnified (x200) sticky spores and the next one up shows a mass of sticky spores adhering to a hair on the leg of the corpse (x100). It's Hammer House of Horrors stuff.

Foxtail’s Filters

Take a close look at meadow foxtail grass’s flower spikes in spring and you’ll find that the youngest have just begun to produce their feathery white stigmas (bottom photo), while more advanced flower spikes are releasing pollen from their dangling stamens (second up from the bottom). Under the microscope the stigmas are revealed at feathery combs of transparent cells whose job is to filter out the airborne pollen (third photo from bottom, x100). Once they’ve trapped a pollen grain it germinates, producing a pollen tube that grows down through the stigma cells (top photo x400), carrying the male cells down to the egg cells in the flower ovary, where they fuse together and begin the process of seed formation. In the top photo you can see the pollen tube emerging from the germinating spherical pollen grain and growing down through a branch of the feathery stigma. There's more on meadow foxtail grass on my other blog at

Saturday, May 16, 2009

Jewels and Sausages

Over at Wight Rambler Rambling Rob recently reported finding spiderwort Tradescantia growing wild, as a garden escape. This plant has interesting flowers, with stamens covered in a forest of hairs so that the centre of the bloom vaguely resembles a spider - if you’ve got a vivid imagination. Under the microscope the hairs have a beauty all of their own, composed of chains of cells that are almost spherical at the tips of the hairs, resembling a string of jewels (second photo down x100). Further down the hair, towards the base, they look more like a string of blue sausages (third photo down x100). These cells have always been favourite subjects for microscopists because you can easily see the cell contents, including the nucleus that contains the DNA which controls the cell and the cytoplasm that streams around inside the cell, which is full of blue anthocyanin pigment (bottom photo x400)

Friday, May 15, 2009

The Most Important Portals on the Planet

If you peel off a thin layer of cells from the surface of a leaf and mount them in a drop of water on a microscope slide, this is what you see – the leaf breathing pores, or stomata. When they open they allow carbon dioxide in and oxygen out. They are, without doubt, the most important portals on the planet. The carbon dioxide that they let in is turned into sugars that form the basis of our food, either directly from plants or indirectly through the domesticated animals that eat plants. The oxygen that they release allows us to breathe. Somehow they have to balance the passage of gases with conserving water, so they open and close depending on how much water is available. Each stoma is made of two lip-shaped guard cells, that bend apart to create a pore when they inflate with water, but collapse to close the pore when they wilt. The one in the top picture (x400) is open, and in the middle picture (x200) one is open and one is closed. The horizontal rows of narrow cells in the bottom picture (x100) are the veins of the leaf, which in this case came from the garden plant spiderwort Tradescantia virginiana.

Thursday, May 14, 2009

Water flea

This rotund little water flea with a long snout, which is a species called Chydorus sphaericus, turned up in a moorland pool in Weardale but it's common in ponds and ditches everywhere. The appearance of water flea species can vary quite a lot, since some can grow extra protective spines on their carapace if they detect the presence of a lot of predatory midge larvae in the water, while others show seasonal changes in shape.

Saturday, May 9, 2009

Blowin’ in the Wind

The male cones of Scots pine are just beginning to release their pollen now, and if you give a branch with ripe pollen sacs a sharp tap it will more or less disappear in a cloud of pollen. Conifers depend on the wind to deliver their pollen, so tend to produce vast quantities of the stuff to ensure that at least a few pollen grains make the successful journey to an ovule, fertilise it and produce a seed. The studio shot of larch pollen here (middle picture), with the yellow pollen sacs releasing pollen that’s landing on the pink young female cone, where the seeds will eventually develop, gives a false impression of the likely success rate. The chance of an individual pollen grain effecting a fertilisation is probably one in several million. The longer the pollen stays aloft, the better its chance in this lottery, so conifer pollen is slung between two balloon-like air sacs that increase its aerial buoyancy. You can see these in the top two microscope photos, at x100 and x400 magnification. They certainly seem to do the job- researchers have collected pine pollen from North American conifer forests on sticky traps mounted on weather ships in mid-Atlantic.