Читать книгу Colin Clout's Calendar: The Record of a Summer, April-October - Allen Grant - Страница 10

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The beds of the kitchen garden at the present moment unintentionally afford an admirable illustration of the main principle upon which most natural colouring seems to depend. In their really beautiful display of bright and gracefully graduated tints they supply us with a picture which, but for its familiar utilitarian character, everybody would stop to observe and admire. There are long sticks of rhubarb, ruddy crimson below, and merging through delicate gradations of pink and white into the golden yellow of the cramped and etiolated leaves above. There is sea-kale, blanched in the stem, and unfolding at the blade into crinkled shoots of an indescribable but very dainty pale mauve or violet. There are beet roots, sprouting with dark Tyrian-red leaves, whose purplish veins persist even in the greening later foliage. Almost every one of the spring plants has more or less of these bright hues, marking them off at once from the common green of full-blown summer leaves. Even on the asparagus one may observe a set of little bluish scales; while the young tufts upon the carrots are pale yellow or golden brown. The reason throughout is a very simple one: all these spring vegetables are perennials grown from a permanent rootstock; and in some cases they have been more or less blanched, naturally or artificially, by growing underneath a loose mass of heaped-up earth. If one looks into the flower-garden, one sees the same thing in the sprouting pæonies, whose rich red foliage is more likely, perhaps, to be admired than the very similar leaves of the beet. All these brilliant colours on spring plants are interesting because of the light which they incidentally cast upon the origin of the equally brilliant and far more definite colours of fruits and flowers.

Those who watch trees and bushes closely must have noticed that the first buds in spring are usually more or less red, or at least reddish or brownish. They must also have noticed that in summer the ends of long growing sprays are likewise ruddy, or purple, or warm brown. Now, at first sight, these facts do not seem to have much connection with another class of facts, such as those noticed above, of which we may take as a typical example the delicate blue or violet tinge on potato-stems allowed to grow in a dark cellar. But when we come to look at them closely, it is clear that they have all one characteristic in common: they are leaves or leaf-stems which are not performing their proper functions. All plants, of whatever sort, when placed in full sunlight develop the active green colouring matter in their leaves—the chlorophyll which enables them to analyse carbonic acid in the air, and to store its carbon as starch in their own sap or tissues. When they are kept in the dark, however, or when they are yet too young to have assumed their proper office, they do not contain any of the green colouring matter, and so they look yellow, pink, or white. The bright hue thus assumed by young or etiolated leaves is due to the oxidation of their materials; and, in most cases where growth takes place from a stock of food already laid by, such oxidation must necessarily go on. It is thus that we get the brilliant red, blue, and yellow colouring of rhubarb, sea-kale, potato-sprouts, beetroot leaves, growing pæonies, or young carrots, as well as of long sprays in hedgerows and on young rosebushes. As soon as the leaves are fully expanded, the green chlorophyll begins to develop, and they rapidly assume their true hue and their active life; but if they are kept in the dark, or prevented from normally developing, they go on retaining their original bright colours for an indefinite period.

It seems most probable that in all cases the oxidation of green leaves, stems, or other parts of plants, produces bright red, yellow, and orange colouring matter. We are all familiar with this fact in the instance of autumn hues, where Mr. Sorby has shown that the pigment is chemically nothing more than an oxidised form of the ordinary chlorophyll. So it is in the case of both flowers and fruits, which are purely expensive structures, produced for the most part from reservoirs of raw material, such as bulbs, tubers, starchy rootstocks, or permanent stems, and thus exactly resembling the red or purple shoots of the pæony, the rhubarb, the sea-kale, and the hawthorn bushes. Every one knows that fruits are at first green, and only grow coloured as they ripen—that is to say, as they oxidise. Mr. Sorby has shown that in flowers, too, the colouring matter is at first green, and exactly resembles that of ordinary leaves; but as they grow older they also get oxidised, and so assume their bright hues.

In fact, the pigment of the petals in many cases is exactly the same, both in colour and in chemical composition, as that of the autumn leaves from which the chlorophyll has disappeared, or of the young spring foliage in which it has not yet been developed. So that, to put it simply, all plants, whether they produce brilliant fruits and flowers or otherwise, have in them all the material necessary for such a display, and could be induced to assume bright hues under proper circumstances, just as our gardeners have made the leaves of geraniums and many other plants do so since the taste for coloured foliage plants set in. Besides, such bright hues are especially apt to appear in the neighbourhood of the fruits or flowers, and do often appear there without any special reason. If, then, in the wild state, they ever happened to show themselves in such a manner as to benefit the plant by attracting birds or insects, we may be pretty sure that the tendency once set up would continue and increase from generation to generation. As a matter of fact, it is manifest that some familiar fruits and flowers only show the tendency even now in a very nascent or incipient form, while others show it in a highly developed degree. For example, in peaches and apples only the sunny side is coloured at all, and that in a very irregular and patchy manner; whereas oranges are fully coloured in every part. On the other hand, pears as a rule hardly show any signs of colouring beyond a slight browning of the peel on one side. Cherries give us every stage—from the merely pink-cheeked whitehearts, to the deep and uniform red of the morella. So, too, among flowers, we may compare the almost accidental pinkiness of the rays in a daisy with the full rich purple of a cineraria. These intermediate cases help perhaps to show us how colour first begins to gather in some particular part, and so forms the groundwork upon which selective action may gradually be exerted. It is not difficult to see how the first few faint streaks of red may begin to dapple the cheek of a ripening fruit, just as they dapple the surface of autumn leaves; and yet when that step has once been taken, it is easy to fancy the subsequent stages by which the colour becomes intensified from year to year, through the constant preference shown by the animal allies of the species for the most conspicuous fruits. In the end, alike with berries and with blossoms, the colouring, which began by being accidental and indefinite, finishes by being perfectly definite and regular.