Friday, November 27, 2009

A Marvel of Miniaturisation

Hard to believe, maybe, but inside a horse chestnut Aesculus hippocastanum bud like this there’s a whole year’s future growth, folded, packaged and ready to be unpacked at the first hint of spring......

A vertical slice through the bud reveals next year's spike of flowers inside, preformed, packed in mass of white hairs (the bud's equivalent of loft insulation), surrounded by an armour of overlapping bud scales and sealed in resin, protected against the rigours of the coming winter.......

Cranking up the magification a little more reveals the sectioned individual flowers. The pink lines around the buds are the sepals and petals, and the elongated yellowish objects inside are the stamens that will produce the pollen that next year's bumblebees will collect...

A transverse section across the flower bud reveals the individual flower buds (surrounded in pink) and next year's leaf stalks (the ring of green circles around the outside of the bud, just inside the overlapping, interlocking bud scales)....

... and at higher magnification in this transverse section you can see the pink sepals and petals of the flower buds a little more clearly. That convoluted wavy green line between the flower bud and the bud scale is the blade of one of next year's leaflets, tightly folded at this stage. The mass of white insulating hairs inside the bud coat the new leaflets when they emerge from the bud in spring, looking in their earliest stages like little furry fists. Something to look forward to.

For a reminder of what those microscopic flower buds will become, hop over to

... and if you want to look even further forward, to next autumn, and see what they'll produce, take a look at

... and for a look at some other buds from different  tree species, hop across to

Sunday, November 22, 2009

Polypody – the fern with the golden sporangia

Some polypody Polypodium vulgare ferns continue producing spores deep into winter and if you turn over a few fronds you’re eventually likely to find these golden cluster of sporangia. Unlike many ferns, the sporangia of this species are not covered by a membrane during their development and under the microscope they resemble nests of golden eggs, or maybe even party balloons if you're in a celebratory frame of mind.

Each sporangium is packed full of spores and when they’re ripe there’s a remarkable mechanism for catapulting spores out into the airstream, that you can read about at

The gaping sporangium at the top of this picture (above) has burst open and has already catapulted out most of its spores. You can still see the spores packed into the surrounding unripe sporangia, through their transparent walls 

Polypody spreads vegetatively with creeping rhizomes, that either grow over the branches of trees or through old walls, and you can see it in its habitat over at

Sunday, November 15, 2009

The Armoured Brigade

Every time I lift the lid of our compost bins to dump another load of kitchen waste a horde of woodlice scurry away in all directions, so I thought I’d catch one and take a closer look under the microscope. It turned out to be the common shiny woodlouse Oniscus asellus. Woodlice are terrestrial crustaceans – relatives of crabs, prawns and lobsters but more closely related to marine isopod (meaning that all the legs are the same length) crustaceans like the one portrayed at

Michael Chinery notes in The Natural History of the Garden (Collins 1977) that woodlice have acquired at least 65 local names, including sow-bugs, tiggy-hogs, sink-lice, slaters and coffin-cutters.

Woodlouse senses are centred around the jointed antennae and simple eyes that have only about 25 individual ocelli – probably enough to detect light and shade and largish moving objects, but probably incapable of forming images with a very high degree of resolution.

The tail segment of a woodlouse is called the telson, flanked by two appendages called uropods , and its shape is often an important species identification feature.

All woodlice have only six pairs of legs in their infancy (when they’re known as mancas) and the full complement of seven pairs, visible here, only appears after their first moult, a day after they’re released from the brood pouch of their mother who carries them around. From below you can see the mouth at the head end, between the antennae .

Woodlice are omnivores but will eat other small animals if they can catch them, so have two pairs of jaws – crushers at the front and lethal-looking pointed ones behind.

The armour is an obvious adaptation to surviving terrestrial predators like spiders but the woodlouse’s main problem is keeping moist, because it obtains oxygen by diffusion over these lung plates at the tail end. Generations of schoolchildren have conducted simple experiments offering woodlice a choice of moist or dry environments but the outcome is never in doubt – in a dry environment a woodlouse will suffocate, for lack of dissolved and diffused oxygen.

Tuesday, November 3, 2009

Swallowtail Scales

Like most long-established university biology departments, Durham University School of Biological and Biomedical Sciences has substantial collections of specimens that have been donated over the years, including a large number of butterflies ........... which offer an opportunity to explore one the the microscopist’s favourite natural objects – butterfly wing scales. These are the wing scales of a swallowtail Papilio macheon which in this old pinned specimen can't match the vibrancy of colour in the living insect portrayed below, but they are still exquisite objects. If you look closely you can see that they vary in shape as well as colour ... notice how the edges of the red ones are more indented than the blue ones. The metallic colours in butterfly scales are the result of optical effects rather than pigments and are produced by ultra-fine grooves in the scales, where light penetrates to different depths and the reflected light waves interact to produce the electric blue interference colours.

Sunday, November 1, 2009


A while back I posted some pictures of Hydra viridis (see showing its remarkable ability to change shape. The pond that I regularly use for collecting small freshwater protists and invertebrates is currently teeming with these tentacled hunters, so I took the opportunity to shoot this short video sequence of this elastic animal in motion.