A Weblog monitoring coverage of environmental issues and science in the UK media. By Professor Emeritus Philip Stott. The aim is to assess whether a subject is being fairly covered by press, radio, and television. Above all, the Weblog will focus on science, but not just on poor science. It will also bring to public notice good science that is being ignored because it may be politically inconvenient.

Monday, December 22, 2003

A touch of winter......

A Winter Solstice/Christmas Essay

"But, since that cannot be, let us draw round the fire,
Munch chestnuts, tell stories, and stir the blaze higher:
We'll comfort pinched robin, with crumbs, little man,
Till he'll sing us the very best song that he can."

['Winter' by Christina Rossetti]

Have you ever wondered why the farmer, having harvested in hazy days the summer crops, plants winter wheat in mellow autumn, so that it germinates only to face the rigours of the cold? It seems a strange practice when much of the vegetable kingdom is closing down operations for the duration. But the farmer has good reason. For certain plants to flower, they need a 'touch of winter' - what we call 'vernalisation'.

A period of winter frost switches development in the plant from vegetative growth to reproduction, thus bringing into play a range of genes controlling spring flowering. The main group of plants requiring this magic touch is the biennials, those that take two years to complete their life-cycle. In the first year, the seed germinates and the plant grows green, often in the form of a rosette of leaves. When the winter frosts blow, these trigger stems and later flowering. Eventually, the plant fruits, seeds, grows old, and dies back, to rot black on the dampening soil - while new plants arise once more, in an eternal cycle, from the germinating seed.

Lots of our more common wild plants act in this special fashion, like the wild carrot of the grey-turfed Downs, with its tiny tap root, pale orange and faintly smelling of the Sunday veg. Our hedgerows are full of such plants - tall foxgloves, red campion, red dead-nettle, strong-smelling garlic mustard, and the piercing spear thistle, although some, like red dead-nettle, perform too as annuals, while others, foxglove and red campion, play the perennial game.

The biennial life-style has many advantages. The hard work of vegetative growth is accomplished first, giving the plant great vigour before it has to use much energy to produce fine flowers and seed. This allows more seeds per plant, which offers a competitive edge in the battleground of field and forest. Where, however, biennials are kept safe from winter's icy finger, say, in mildewed greenhouses or warmer spots, they often fail to flower, turning into perennial green plants, growing on for many years, without fulfillment or fruition.

Biennials, as well as many perennials, also bear another, posher name. They are called 'hemicryptophytes'. This tricky term is ascribed to those plants that survive the adverse conditions of winter by protecting sensitive growth organs at, or very near to, the surface of the soil. They are best observed as rosette plants - the common dandelion, the rough hawkbit, or the cat's ear. As many gardeners know to their cost, such a life-style choice also protects the offending 'weed' against cutting and mowing, not to mention grazing.

Other plants, by contrast, have different strategies for surviving the 'touch of winter'. Daffodils, the crocus, and our chalk grassland orchids are 'geophytes', avoiding the cold snug beneath the turf as bulbs, rhizomes, tubers or corms. Yet others are true annuals, or 'therophytes', surviving the winter in the earth as seeds. Unlike biennials, these complete their life-cycle in a single, swift, sweet year, shedding new seed in late-summer or early-autumn, which then lies dormant in the frozen ground until the nightingale and the cuckoo call once more. They are the weeds of bare ground, or of disturbed land, like the small nettle, Urtica urens (that childhood chastisement, the stinging nettle - Urtica dioica- , is, by contrast, a perennial and aptly named Urtica!).

Finally, of course, there are the woody plants, from tiny cushions and larger shrubs to the tall trees of the ancient forest. These are 'chamaephytes' - strong-scented thyme - or 'phanerophytes', like the knotted English oak, and they must protect their exposed organs in different ways, by scales or special coverings.

This fascinating way of looking at the plant kingdom, taking into account the response to the 'touch of winter', was developed in the early part of the 20th Century by a renowned Danish botanist, called Raunkiaer, and it is fondly known among ecologists as Raunkiaer's Life-Form System. Every ecosystem has its own special mix of life-forms, a mix reflecting the selective pressures in each habitat. Open, windswept, sheep- and rabbit-grazed, springy-turf Downs, for example, carry mainly 'hemicryptopytes', each well-protected against eager teeth, trampling feet, swaling fire, and winter frost.

Personally, I have a lot of the 'hemicryptophyte' and the 'geophyte' about me. The 'touch of winter', which has just swept violently across the country, is the moment to go to ground in the deep dark of the death of the sun, when the 'golden bough' pierces Balder's heart - "Fear not, Sol Invictus will be born again!" But for now, it is time to "draw round the fire, munch chestnuts, tell stories, and stir the blaze higher" (or, to huddle by the radiator, crunch crisps, watch the box, put on that gaudy sweater, and turn up the thermostat!).

With a glass of crusty port in hand, and a ripe stilton on my knee, I'll toast the wonderful adaptability of Nature in the warmth of my own hibernation - until the 'touch of winter' is past. A Merry Christmas to you all, wherever your own snug burrow.


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