Tuesday, April 28, 2009

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.

Thursday, April 23, 2009

Water bears in space - and on my garage roof

The cushions of moss that grow on my garage roof are a rich source of microscopic wildlife, including these little tardigrades, also known as ‘water bears’ or ‘moss pigs’. These are up to a fifth of a millimetre long, with eight legs that end in claws that allow them to clamber amongst the leaves of mosses. Tardigrades feed on mosses in the same way that greenfly feed on larger plants, by spearing the plant with a hypodermic syringe-like stylet and draining out the sap - you can see the green cell contents inside the gut of one of the tardigrades in these pictures. The most amazing thing about tardigrades is that they are virtually indestructible. When their habitat begins to dry out they develop into a barrel-shaped resting cyst call a ‘tun’, and in this state can survive in a state of extreme dehydration for decades. While in the tun stage they can survive extreme environmental conditions – even extreme vacuum and cosmic radiation in space – see http://tardigradesinspace.blogspot.com/

Wednesday, April 15, 2009

Crustacean Castanets

Our garden pond is currently full of these little Cypris sp., a.k.a. seed shrimps, that belong to a subclass of crustaceans called ostracods. Each animal resembles a water flea enclosed within a pair of hinged shells. When they’re swimming they look like animated castanets (see video clip), when they’re at rest they look like a minute bean.

Monday, April 13, 2009

Bubbling stones

The pebbles in the pools left by the falling water level in the upper reaches of the River Wear were bubbling in the bright spring sunshine this morning. Scraping some of the thin film of slime from the stones onto a microscope slide revealed the cause – millions of minute, photosynthetic diatoms, producing oxygen bubbles. In amongst them I found several amoeba, like the one shown in the second-from-top photograph, grazing on these underwater meadows.

Saturday, April 11, 2009

Lifting the edge of the blanket

I spent some time yesterday fishing the blanket weed out of my smallest pond, and took the opportunity to take a look at the microscopic organisms that live in it. There were vast numbers of ciliate protozoans, about a twentieth of a millimetres long, whizzing around at a tremendous speed. They are propelled by fringes of microscopic hairs that beat in rhythm and they can change direction instantly, so they can be tricky to photograph. The ciliate in the picture here might be a species of Oxytricha, but I’m not totally sure about that. The green objects inside it are algae that it has ingested. The two videos show a large rotifer that was attached to the blanket weed, with its ‘wheel organs’ (rings of rhythmically beating cilia) creating a vortex that sucks food into its constantly chewing jaws. These animals always remind me of twin-head electric razors. Blanket weed can be a pain in ponds, but it supports a vast array of minute organisms that are the base of a food chain for larger animals.

Friday, April 10, 2009

Sticky Jack

Came in from weeding in the garden with bits of goosegrass Galium aparine stuck to my clothes. We used to call it 'sticky Jack' when we were kids, and lobbed handfuls of the stuff at each other on the way home from school. It's the covering of tiny hooked hairs all over the plant that act like Velco, fixing it to fabrics. The hairs on the stem are shortish and curved, but those on the leaves are like fish hooks - when you look at them under the microscope.

Thursday, April 9, 2009

Inside the Stomach of a Predatory Plant

The carnivorous Nepenthes pitcher plants that I grow in my conservatory are producing new leaves and pitchers, and one has caught its first fly. Deep inside the pitcher you can see the drowned insect. The dark spots on the inner wall of the pitcher are the plant’s digestive glands which secrete the enzymes that slowly dissolve their prey. The photomicrographs show the glands in the wall at x40 and x100 magnification. They not only secrete enzymes, but also absorb the products of digestion which provide the plants with essential nitrogen, for producing its own proteins. This – in effect – is the plant’s stomach.

Tuesday, April 7, 2009

The Inner Workings of an Onion

Onions have long been a favourite source of material for microscopists who want to explore the inner workings of a cell. Peel apart the onion bulb scales and it's easy to strip away the skin of cells that coats the scales; mount these in water on a microscope slide and large, brick-shaped translucent cells are easily visible and reveal the nucleus, that contains the DNA and controls the life of the cell. The centre of the cell is occupied by a large fluid-filled vacuole, with cytoplasm squeezed between it and the cell walls. Watch for a while and it soon becomes apparent the the cytoplasm is constantly streaming around the cell walls, carrying with it minute organelles like the mitochondria, they provide the energy that keeps the cells alive. Sometimes the cytoplasm is drawn out in strings across the vacuole, like stretched-out chewing gum. The whole of the cell is in a constant state of motion. So, next time you're about to chop an onion and chuck it in the frying pan, pause for a moment and contemplate the marvellous process shown in these video clips, which is going on in hundreds of thousands of cells in the living onion in your hand.

Saturday, April 4, 2009


In Victorian times it was socially acceptable to possess books devoted to smut – provided that the smut was of the fungal variety. It’s hard to imagine that a book entitled Rust, Smut, Mildew and Mould: An Introduction to the study of Microscopic Fungi would sell well with the general public today but M.C. Cooke’s volume of the same name, published in 1870, apparently did. “In these latter days, when everyone who possesses a love for the marvellous, or desires a knowledge of some of the minute mysteries of nature, has, or ought to have, a microscope,” Cooke began confidently, “a want is occasionally felt which we have essayed to supply”. His book seems to have satisfied that want, since the preface to the second edition states that it was produced as a response to “demands from the public encouraging the publisher to proceed with a new edition”. So more smut – together with rust, mildew and mould, is what the public got. One of the plates illustrates the bright coloured patches that appear on bramble leaves, caused by the fungus Phragmidium violaceum, showing its distinctive club-shaped resting spores (teleutospores) that are released from purple pustules on the leaf undersurface (middle left illustrations). I scraped some of these onto a microscope slide and photographed them – a comparison with the plate from Cooke’s book shows that his illustration is pretty accurate. Wight Rambler has recently written about brilliantly coloured bramble leaves at http://wightrambler.blogspot.com/

Microscopic Mohican

Our Victorian forebears amused themselves with family evenings around the piano or, if they were scientifically inclined, around the microscope. Driven by the desire for self-improvement and by scientific curiosity, it was possible for these amateur microscopists to make genuinely original scientific discoveries - and many did, after first honing their skills with the help of books like those illustrated above: Philip Henry Gosse’s Evenings at the Microscope; the anonymously published Half-hours in the Tiny World; M.C Cooke’s Rust, Smut, Mildew and Mould: An Introduction to the study of Microscopic Fungi ; and the Reverend J.G.Wood’s Common Objects Under the Microscope, a rather shambolically organised volume with attractive colour plates. A favourite method of generating specimens for microscopy was to create an infusion of rotting plant material, and sample it at regular intervals. A whole succession of minute, single-celled organisms (then called protozoa, now known as protists) appeared; a single infusion could provide weeks of amusement for the whole family. I set up an infusion of decaying grass in a jar of water about three weeks ago and the predatory protist above, that goes by the name of Litonotus, is thriving in the scum that’s floating on the surface of the water. It’s propelled by a fringe of rhythmically beating hairs (cilia), rather like a Mohican haircut, at the front end and can change shape readily, engulfing food particles in the distended end of its body. It never rests for a moment – hence the rather blurry pictures. The largest examples are about a quarter of a millimetre long – which is big for a protist.

Wednesday, April 1, 2009


I suffered my first sting of the season today while I was hacking down nettles in the garden, which offers a tenuous excuse to celebrate the achievements of Robert Hooke FRS, the father of English microscopy. Hooke was born in Freshwater on the Isle of Wight in 1635 and in a varied career, that included research in mechanics, astronomy and architecture, produced perhaps the most celebrated book on microscopy: Micrographica, or Some Philosophical Descriptions of Minute Bodies made by Magnifying Glasses withe Obervations and Inquiries thereupon. Samual Pepys bought a copy and commented ‘took home Hook’s book of microscopy, a most excellent piece’, as well he might, as some of Hooke’s descriptions and detailed, exquisite engravings would not be out of place in a biology text book today. Compare his engraving of the stinging hairs on a nettle leaf , above, with the photograph of the hairs on the leaf of the nettle that stung me today – astonishingly accurate, when you consider the rudimentary nature of the microcope lenses he was working with nearly four centuries ago. The nettle sting is a remarkable structure – a long, tapered hollow cell on a pediment (or a 'bladder' as Hooke called it), filled with irritants under pressure and tipped with a minute hooked glass bead that snaps off at the slightest touch, turning the hair into a hypodermic syringe. After watching the whole processes of stinging himself under his microscope, Hooke recorded the following:”The chief thing therefore is, how this plant comes, by so light a touch, to create so great a pain; and the reason of this seems to be nothing else, but the corrosive penetrant liquor contain’d in the little bags or bladders, upon which grow out those sharp syringe-pipes......”. All of Hooke's wonderful engravings from Micrographia can be viewed at http://archive.nlm.nih.gov/proj/ttp/hooke_home.html