Читать книгу Colin Clout's Calendar: The Record of a Summer, April-October - Allen Grant - Страница 5

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In spite of the severe and long-continued cold, the trees and flowers themselves seem to have made up their minds that we are to have an early spring—at all events here in the west country. The difference in the general forwardness of vegetation between the two great slopes on either side of England is this year extremely marked. In Kent and Sussex the buds are still closely covered in their dusky winter coats; the flowers (save primroses) have hardly begun as yet to straggle here and there in a tentative way through the long-frozen soil; and there is scarcely a sign anywhere among the meadows or copses that spring has set in at last. But in the south-western counties it is quite otherwise. The gardens here are gay already with bright golden borders of crocus; snowdrops are flourishing in the open air; and jonquils and daffodils are sending up their pale yellowish-green leaves, enclosing their tall scapes with the papery spathes half revealing the slender buds within. On the horse-chestnut trees the dark gummy sheaths are just beginning to open under the pressure of the wan and growing leaflets which they have covered through the winter season; the hardier shrubs are already well in leaf, though the blades are still folded together or only half expanded as yet; and even on the hedges the whitethorns are showing signs of life, the little fresh pink scales bursting through their brown and withered coverings, or even sometimes showing a tiny green tip at the very end of a growing bough. When I break off the smaller branches I can see by the bright green and sappy look of the inner bark that the bushes are actively engaged in putting forth chlorophyll, and that a few days more of these warm westerly breezes will bring out the buds into leaves, at least in the sheltered southern hollows and combes.

This wide difference of climate between the Atlantic slopes—open chiefly to the influences of the Gulf Stream and the warm breezes which blow across it—and the eastern half of Britain, which lies right in the teeth of the Siberian east winds, has even stamped itself permanently on the character and distribution of our flora. Many of our plants of warmer types are only found in the south-west. The high moor, on which I have come out to-day for my morning’s stroll, covered even now by little white and short-stemmed daisies—they will grow taller and pinker as the spring advances—is Claverton Down: and Claverton Down is the only station in England for a particular species of hairy spurge, of which in fact I am now in search.

It is not in itself a particularly interesting plant, being very little different from the other spurges, all of which are mere rank woodland or wayside weeds, with curious green and black flowers, more noticeable to the botanist than to the ordinary observer. But the fact that it is found nowhere else in Great Britain except on this spot, one of the warmest and most forward hill districts in the south of England, gives it an adventitious value for every collector, and a real one for the student of botanical history. Evidently, the hairy spurge grows here, and only here, because, being a mountain species of warmer climates, Claverton Down is the only hill in Britain at once high enough and warm enough to suit it. This explanation sufficiently accounts for its absence elsewhere, but not quite for its presence here. How did it get from the Continent to Claverton Down?

If the occurrence of the hairy spurge in England were an isolated case, we might suppose that it had been accidentally imported by man, or that the seed had been blown here by the wind, or that it had been carried over by clinging to the feet of birds. Such accidents do undoubtedly account for many special facts of distribution and acclimatisation—for example, all oceanic islands, as Mr. Wallace has amply shown, are peopled with mere waifs and strays of various distant faunas and floras in just this fragmentary fashion. But the case of the spurge is by no means a solitary one; on the contrary, the south-western districts of England and of Ireland are full of peculiar species found in no other parts of Britain. Thus a pretty little purple lobelia, a familiar plant in southern France and Spain, is alone found with us on a single common near Axminster in Devon. So, too, Cornwall and the Scilly Isles are rich in southern forms. The arbutus, or strawberry tree, which grows so abundantly, with its white bell-shaped blossoms and its pretty red berries, over the Provençal hills, is met again quite unexpectedly on the mountains of Kerry. The Mediterranean heath—that beautiful white scented heather which every visitor to the Pyrenees has gathered in spring among the pine-woods of Pau and Arcachon—turns up once more a thousand miles off in Connemara. Altogether, no fewer than twelve Spanish species are found in south-western Ireland, and in no other part of Britain; while similar species extend to Pembrokeshire, or are peculiar to the south-western peninsula of England and the Mediterranean or Spain and Portugal. A special Portuguese slug and a few other southern animals are also found under the same conditions.

Clearly it would be absurd to set down so many coincidences between these warm western regions of Britain and the Continent to the chapter of accidents alone. Our south-western flora is undoubtedly on the whole a Spanish and Pyrenean flora in its general aspect, with a large intermixture of northern forms. Sometimes the south European species linger on only in a single spot, like the hairy spurge at Claverton Down and the purple lobelia at Axminster; sometimes they spread over wide areas, and hold their own manfully against the intrusive Scandinavian types. Of these curious phenomena the probable explanation is suggested in a passing hint by Mr. Wallace.

The southern plants are probably relics of the flora which lived in Britain before the glacial epoch. At that time, as our geologists are agreed in believing, Great Britain and Ireland formed part of the continent of Europe, to which they were united by a broad belt of land, extending over the present bed of the English Channel and the Bay of Biscay. As the ice pushed its way southward, the northern plants migrated before it to regions which were made more fit for them by the change of climate due to the glaciating conditions. Thus the arbutus, the Mediterranean heath, the various warm types of saxifrages, of butterwort, and of spurge, must have had a range from Killarney and Cornwall to the Pyrenees, the Apennines, and Crete. It is noticeable, too, that according to the map recently published by Dr. Geikie, the south-west of Ireland and England are just the parts of Britain which escaped glaciation during the height of the great ice age.

Very possibly, however, these warmer plants may at first have been driven quite southward, beyond the existing limits of Britain, but may afterwards have moved northward again as the ice melted. When the connecting lands were washed away by the waves, or submerged by alterations of level, the arbutus, the lobelia, and the scented heath would be stranded, so to speak, in a few warm corners of England, Wales, or Ireland, and would be separated by many miles from all other specimens of their race elsewhere. In some cases, no doubt, they would be killed off by the intrusive Scandinavian forms, which always show a singular power of living down all opposition; and as still warmer types would finally occupy the lowlands of southern France, when the ice age was quite over, it happens now that these insulated plants live in the mountain districts only—the Pyrenees, Auvergne, and the Mediterranean islands, as well as in the hill regions of Kerry and Cornwall. The warmth derived from the Gulf Stream and the insular position has put the west coasts of our islands on a practical equality with mountain-countries many degrees south of them. The same climatic peculiarities which make the horse-chestnuts bud a month earlier in the valley below me than on the east coast have enabled the hairy spurges to live on for ages among the combes and dells of this broken oolitic down, in spite of their total separation from the main body of their congeners elsewhere. Warm nooks like Bath and Bournemouth, in fact, form as it were climatic islands in the midst of our average British temperature; while in the sheltered spots of the Isle of Wight the Italian arum and the woodland calamint live on as wild plants, whereas they have long since been totally extinguished by the cold in all the rest of England.