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 http://news.bbc.co.uk/1/hi/sci/tech/8049954.stm

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.

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 http://cabinetofcuriosities-greenfingers.blogspot.com/

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)

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.

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.

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.

Klingon Warship

I found this little rotifer called Keratella, looking like an armour-plated Klingon warship, or maybe a medieval chain-mail glove, in a moorland pool about 500 metres above sea level in Weardale. Under the microscope it looks like a swimming claw, propelled by those whiskery looking hairs that you can see between the armoured ‘fingers’, which also serve to produce a water current that sweeps minute food particles into its jaws. The red spot is a light-sensitive eye spot. Most amazing of all, that egg-shaped object being towed around behind one of them is an egg – but not just any old egg. These animals reproduce by cloning themselves and never reproduce sexually, so the individual inside the egg is an exact genetic copy of the adult animal it’s attached to. When I peered down the microscope, I could see this animal’s alter-ego squirming inside the egg, ready to hatch. Keratella is about a quarter of a millimetre long.

Living sponge

Bright green patches of bog moss (Sphagnum) thrive in wet hollows on the fell tops. Step into one of these and you’ll suddenly find that you’ve got a boot full of water, because this moss acts like a living sponge. Each plant constantly grows from its apex and dies from its base and the accumulated weight of living plant crushes layers of dead moss underneath, which ultimately form peat. It’s the plant’s ability to retain water, even in dry summers, that makes Sphagnum bogs such important wildlife habitats for moisture-loving wildlife. You need to look at the minute leaves under the microscope to see how they do this. Magnify the leaves a little and you can see that each leaf is a network of cells. Increase the magnification a little more and two kinds of cells are revealed – green photosynthetic ones (the living part of the leaf) and empty, transparent dead ones. The photosynthetic cells form a living network, enmeshing the dead ones. Increase the magnification further and you can see the structure of each dead cell, it’s shape maintained by beams of thick cell wall material, with a hole in each cell wall. Once these dead cells fill with water capillarity holds it firmly in place. Squeeze the moss and water flows out like water from a sponge. Tread on one of those bright green patches and the water fills your boot..........and then it's wet socks for the rest of the walk.