Delphi collected works o.., p.738
Delphi Collected Works of Grant Allen, page 738
By-and-by, however, the earth’s crust began to sink in western Europe, as it is sinking now in Scania and the bed of the southern Baltic. Slowly the great Atlantic plain disappeared below the waters, leaving only the mountain-tops and higher plateaus as islands above the sea-level. First the two lateral valleys of the old lake-system were flooded, cutting off Ireland and the western Hebrides as two large and compact islands, considerably bigger than they now remain at the present day. Then, doubtless, the North Sea and the Channel were overflowed, leaving only a narrow neck of chalk downs as a connecting link between Kent and Picardy, which the waves gradually beat down and at last destroyed. The cliffs of Dover and Cap Blancnez, of Beachy Head and Dieppe, now mark its limits. Still the Bristol Channel remained an open valley, and Scilly was united to the Cornish peninsula. Next, Scilly and the Channel Islands went; while the Hebrides and the western coast of Scotland broke up into a number of separate islets, only the granite crests of the higher mountain-ranges now overtopping the water in long lines, while the lateral valleys became the straits which separate the various members of the different archipelagos from their nearest neighbours. Any one who has once yachted down the broken ridge of the Outer Hebrides cannot fail to have noticed that they seem but the summits of a vast sunken range, jagged and beaten at the outer edge by the ceaseless dash of the Atlantic. Last of all, apparently, went Anglesey, Wight, and the coastwise eyots, as well as the Bristol Channel. On the protected eastern shore of Britain generally, the low slopes have survived well enough, and patches of shingle and sand, like the Dogger Bank, still mark the position of the higher sunken lands; but on the west and north the open Atlantic has eaten away all but the most sheltered plains, and cut its way at all exposed points into the heart of the hills, giving rise to the magnificent cliff scenery of Cornwall, Kerry, and the western Highlands. If you stand upon the shore of Coboe Bay in Guernsey, and look at low tide across the vast floor of jagged and water-fretted granite rocks which line its bottom, you will see with what force the waves have wormed their way over all the lowland; and they will only halt when they have planed down the whole of the island, as they have already planed down the lesser land which once stretched out to northward beyond the solitary pinnacles of the Casquets.
When all these changes had taken place, the stray members of the southern flora in Cornwall, Devon, Kerry, and Connemara would find themselves quite cut off from their fellows in the Mediterranean, the Pyrenees, and the Asturias. For the water has eaten away almost all the plain of the Bay of Biscay, save only a comparatively insignificant angle between the Loire, the mountains of Auvergne, and the roots of the Pyrenees; and it has left the high and bleak granite moorland of Brittany jutting out alone into the western sea. But Brittany looks northward, and is open only to the chilliest winds; while its fair share of the Gulf Stream is diverted by currents due to the lay of the land in Cornwall. Moreover, the great bight of Biscay distracts and upsets the old run of the water, so that the whole shore of France from the Garonne northward is really colder and less equable in temperature than Cornwall and Kerry, or even than the average of our own western and southern coast. The Vendée is a chilly marshland; Bretagne Bretonannte is a high and wind-swept heath. On the other hand, our extreme south-western peninsulas and islands are bathed on every side by the warm water of the Gulf Stream, and so possess an unusually mild, damp, and equable climate. Every one has heard of the semi-tropical vegetation of palms and aloes which flourishes in the open air at Tresco Abbey in the Scilly Isles. Here, then, we have exactly the conditions under which the southern plants, though beaten back to the very base of the hills, might still manage to keep up a precarious existence in a few scattered and sheltered nooks. And that is exactly what they have done. Separated from all the rest of their kind, exposed to occasional hard winters or heavy frosts, and slowly dying out under our very eyes, they have yet left here and there a few isolated descendants to tell the story of their origin and their failure. Curiously enough, these little lingering colonies of Mediterranean plants exist only on the southern and western slopes, among the cliffs and combes and bays which face and overlook the submerged lands whence their ancestors were driven by the advancing sea. So oddly do they confine themselves to the islands and the most insular peninsulas that their geographical distribution almost looks like a preconcerted arrangement.
Thus we may observe once more that one little islet of the Bristol Channel alone preserves the red pæony. Holyhead Island has half a dozen rare species. The Jersey centaury, Pelisser’s linaria, and several other southern flowers have died out everywhere save in the Channel Islands. Scilly shares with them in the sand bird’s foot. The Irish Arran and other Irish islands have many peculiar species; and a few southern types even reach Bute and the western Highlands; for, as every one knows, Rothesay has a climate almost as warm as Torquay. So, too, with the peninsulas. The Lizard, with the most equable temperature on the English coast, is a perfect mine of wealth to the botanist. It has three peculiar southern clovers, and lots of other rarities. Penzance, at the very horn of Cornwall, has five or six specialities. The position of Kerry gives it a climate like that of Finisterre, with the appropriate flora. Wild madder belongs only to a few headlands of Pembrokeshire, the Damnonian peninsula, and the south-west of Ireland. Torquay, on the promontory of Hope’s Nose, shares a southern buplever with the Channel Islands. Babbicombe has a species almost to itself. Corfe Castle, in the so-called Isle of Purbeck in Dorset, divides a Spanish heather with Cornwall and the West of Ireland. One kind of rest-harrow, after getting up from the Pyrenees as far as the Channel Islands, then positively takes a second spring to the Mull of Galloway. As to the number of Mediterranean plants which are found in Britain only in Devon and Cornwall, or in Kerry and Connemara, or in both, I spare you the recital of them. Even the more inland and moorland types, which each survive on one high common alone, answer to the same law; for they occur on the warmest moors, in the neighbourhood of the sunniest south-western slopes. Thus the Cheddar pink grows in a single basking hollow heated by radiation from two great walls of limestone rock upon the western flanks of Mendip; the purple lobelia loiters on a bright upland near the warm valley of the Devonshire Axe; the white sedum struggles on upon the edge of Malvern; and my hairy wood-spurge here battles hard for life on Claverton Down, close to the steaming basin of the old Roman Thermæ at Bath.
And so I end where I began. My sermon has led me far afield; but, like a good preacher, I have come back to my text. I have only touched lightly upon the simplest and least technical proofs; but when the whole evidence is put together — as I do not pretend to put it together off-hand, sitting here cross-legged on the edge of Wansdyke — there can be very little reasonable doubt that this is something like the way in which the hairy wood-spurge first found its way to the Prior Park Lane. So I have gathered my little morsel tenderly and carefully, not injuring the little plant more than I can help by my clumsiness; and I hope all future botanisers will do the same, in order to aid in preserving and handing down to after ages this interesting fragment of old English history, kept green and vital for us all in the tiny blossom of a wayside weed.
III. STRAWBERRIES.
Fig. 17. — The Wild Strawberry.
Side by side in our English hedgerows in early springtime there grow two sister plants, almost exactly alike in foliage, flower, and all other points except the fruit, but differing widely from one another in that solitary, and to us essential, particular. One of these plants is the wild strawberry, the other is the little three leaved, white potentilla. It is not often that a parent species and its more developed offspring survive together in the same district, but this is almost certainly the case with these two small English wayside flowers. Indeed, the similarity between them is so close that even the most unobservant passers-by have been greatly struck with it; and the common native English name of the white potentilla— ‘barren strawberry’ — bears witness to the striking character of the family likeness. Perhaps one ought rather to go a step further, and to say that, while the most unobservant have perceived the relationship, only the more observant have ever discovered the distinctness of the two plants. Nothing is more ordinary than to hear casual townsfolk exclaim that though there were lots of strawberry blossoms a little while ago in such-and-such a spot, there are no ripe strawberries to be seen now that the time has come for picking the fruit. In such cases, careful examination will generally show that the spot is really covered by white potentilla plants, whose little starry flowers were easily mistaken by the world at large for true strawberry blossom. Though there are some marked distinctive features even in the flower, to which I shall presently recur, it is in the fruit alone that the two plants really differ sufficiently to attract the attention of an unbotanical eye. But here the difference is one which touches humanity on a very keen point indeed, for the strawberry blossom sets at last into a sweet and pulpy berry, while the potentilla blossom sets only into a small head of dry and unpalatable nutlets. How the edible fruit has developed from the inedible seeds is the question which I propose briefly to investigate in the present paper.
To get properly at the ancestry of the strawberry, we ought first to begin with the potentillas at large, for a most important part of our evidence consists in the fact that the white potentilla varies from the central type of its race in nearly all the same particulars as the strawberry plant. In other words, we have to show that the ancestors of the strawberry had already acquired most of their existing peculiarities while they were still white potentillas, and that they have only then varied so far as to have added to that white potentilla type the one extra peculiarity of a red and juicy berry. Our systematic botanists, indeed, will tell us that while the one plant belongs to the genus Potentilla, the other plant belongs to the totally distinct genus Fragaria; and they imply, therefore, that the differences between the real strawberry and the barren strawberry are far greater than the differences between the barren strawberry and the other potentillas. I hope in the sequel to show, however, that it would be far easier to develop a strawberry out of a white potentilla than to develop a white potentilla itself out of any one among its yellow allies; and therefore that the systematic classification is a faulty one, and the popular classification a correct stroke of half-unconscious scientific intuition.
The potentillas are a group of very lowly and primitive roses, the earliest and simplest surviving members of the great and world-wide rose family. Our common English cinquefoil may be accepted as a good typical instance of the whole group. Cinquefoil is a pretty tufted creeping plant, whose small golden flowers, like yellow roses in miniature, star the waste grass-plots by the sides of lanes and highways everywhere in Britain during the summer and autumn months. Its leaves, as the very name denotes, consist of five separate spreading leaflets, all springing from a common point, and radiating round it as a centre like the fingers of a hand. The flowers, as usual in most very simple and primitive plants are bright golden yellow, and they closely resemble the equally early blossoms of the buttercup, which similarly form the starting point of another great and varied family. Originally, there is good reason for believing, all flowers were of this same bright golden yellow hue; and those of them that have since progressed to other colours, under stress of special insect selection, have passed through regular gradations of white, pink, red, crimson, purple, and finally blue. Some flowers still remain at the ancestral yellow stage; others have got on as far as white or pink; yet others have attained the stage of crimson or purple; and a very few, the most advanced of all, have even reached the culminating glory of deep blue.
We have several other yellow potentillas in England besides the cinquefoil, and some of these have varied a good deal in foliage or other points from the central form. Nearest of all to it stands the small tormentil, so frequent upon heaths or other moors and uplands; for the main distinction between them lies in the fact that the cinquefoil has usually five large petals, while the tormentil has usually only four. This difference, however, is by no means always constant, for on the one hand it is easy to find stray flowers of cinquefoil with only four petals, while on the other hand the first flower on each stalk of tormentil has only five. There is an intermediate form, too, which exactly splits the difference between the two plants in every respect; and one can hardly doubt that tormentil is in reality only a very slightly altered form of cinquefoil, grown woodier and more dwarfish from its peculiar upland situation, and with one of its petals suppressed through gradual failure of constitutional vigour. The frequency with which the first flower on each stem recurs to the original five-petalled form, while the material to spare remains abundant, is very significant: the later flowers, as the material for their formation runs short, have generally to be content with only four petals each.
More divergent types of potentilla than these are the forms which have their leaves (to use the technical term) pinnately, not digitately, divided — that is to say, with the separate leaflets arranged along two sides of a central leaf-stalk instead of radiating from a common point; and though the white potentilla and the strawberry belong rather to the latter or digitate division, I shall yet enter briefly into the nature of the pinnate section, for the sake of the light which it throws by analogy upon the evolution of our own proper subject. Commonest among the potentillas of this divergent group in northern Europe is the trailing silver-weed or goose-weed of our English roadsides, a pretty, long-leaved plant, with a silvery underside, and bright golden flowers springing from rooted joints on its creeping runners. A rarer plant is the shrubby potentilla, which grows in bushy or stony places, especially on mountain sides, and has accommodated itself to its special situation by acquiring a stout woody stem. This species also has a yellow flower. But there are two other pinnate-leaved English potentillas whose blossoms have long since changed colour under the selective influence of their insect fertilisers. One of these is the marshy comarum, a perennial which grows in peaty or boggy places, and has assumed a dingy purplish-yellow hue, to suit the eyes of marshland insects. It is very noticeable that waterside flies do not seem to care for yellow, and most waterside flowers are therefore pinkish, purplish, or white. Thus the water-crowfoot and the mud-haunting ivy-leaved crowfoot have become white, while all our other native buttercups remain yellow. In the group of bennets or Geums, closely allied to the potentillas, we find a still closer analogy, for the roadside herb-bennet or common avens is yellow like cinquefoil, but the marshy water-avens has exactly the same dusky purplish-yellow tint as the marshy comarum. The other pinnate English potentilla, found wild with us only among the clefts of the Breiddin Hills in Montgomeryshire, is a mountain species with handsome and conspicuous white blossoms; and this also is in striking analogy with similar facts elsewhere, for mountain species usually rise higher than their neighbours in the scale of colour, owing to the keen competition between the flowers for the visits of those rare fertilisers, the butterflies, which sail further up mountain heights than the bees and other meadow honeysuckers. For example, some Alpine buttercups are snowy-white, while most of their lowland congeners are simply yellow.
With the side light thus cast upon our subject by the analogy of the pinnate potentillas, let us hark back to the digitate cinquefoil once more, and ask by what steps some such early ancestral form gave origin to the common predecessor of the true strawberry and its barren sister. The cinquefoil, we saw, had five leaflets to each leaf, but the strawberry and the white potentilla have three only. This is one of the marked points wherein these two plants differ from the other potentillas, and agree with one another. But though the trefoil leaf is a matter of some importance, as indicating community of origin, it is not difficult to understand how it has been developed from the primitive cinquefoil. The exact number of leaflets in a leaf is always rather variable, depending partly on the mode of growth of the plant, and partly on the amount of available material. Thus, in the allied tormentil the lower leaves have five leaflets, but the upper ones have usually three only. In the spring potentilla, a rare English species, the lower leaves have seven or five, and the upper ones five or three. Again, where a species creeps along the ground, it is apt to have long pinnate leaves with many leaflets, as happens, for example, with silver-weed and many similar plants. But where the leaves grow habitually among tall grass or choking wayside weeds, the number of leaflets is very apt to be reduced to three, as happens, for example, with clover and lotus among the pea-flower tribe, and with wood-sorrel among the geranium tribe, many of whose allies have long pinnate leaves with numerous leaflets. Now, the strawberry and the barren strawberry differ conspicuously in habitat from the other potentillas in the fact that they grow mainly among grass, on banks, or in hedgerow thickets. Hence it suits them best to raise their trefoil leaves on tall stalks above the neighbouring herbage, and thus to get at the light and air which they require for their proper growth. Natural selection has easily brought about this result, because in such situations those potentillas which raised their leaves highest would best survive, while those which trailed or crept closely along the ground would soon be starved out for want of carbonic acid (the raw material of growth) by their surrounding competitors.
Fig. 18. Flower of Wild Strawberry.
Fig. 19. Flower of White Potentilla.
In another direction the ancestors of the strawberry and of the barren strawberry also diverged from their cinquefoil predecessors, and that was in the peculiar colour of their flowers. For some reason rather difficult to decide, the petals have changed from yellow to white. Difficult to decide, I say, because we do not exactly know what are the insects which the strawberries set themselves out especially to please or what is the peculiar nature of their specific taste. But, as a rule, this change from yellow to white petals is an ordinary concomitant of higher development, and it probably accompanies some change in the insects to which fertilisation is generally due. Our own native species have got no further in the upward course of development than white; but two allied East Indian forms with digitate leaves, cultivated in our flower-gardens, the Nepaul potentilla and the purple potentilla, have risen as far in the scale of coloration as crimson and deep red.
