Delphi collected works o.., p.747
Delphi Collected Works of Grant Allen, page 747
The plum scarcely differs from the cherry in anything important except the colour, size, and shape of the fruit. It is, as we have already noted, a cultivated variety of the blackthorn, in which the bush has become a tree, the thorns have been eradicated, and the fruit has been immensely improved by careful selection. The change wrought in these two wild bushes by human tillage shows, indeed, how great is the extent to which any type of plant can be altered by circumstances in a very short time. The apricot is yet another variety of the same small group, long subjected to human cultivation in the East.
Peaches and nectarines differ from apricots mainly in their stones, which are wrinkled instead of being smooth; but otherwise they do not seriously diverge from the other members of the plum tribe. Indeed, though botanists rank the apricot as a plum, because of its smooth stone, and put the peach and nectarine in a genus by themselves, because of their wrinkled coating, common sense shows us at once that it would be much easier to turn an apricot into a peach than to turn a plum into an apricot. There is one species of nectarine, however, which has undergone a very curious change, and that is the almond. Different as they appear at first sight, the almond must really be regarded as a very slightly altered variety of nectarine. Its outer shell or husk represents the pulpy part of the nectarine fruit; and indeed, if you cut in two a young unripe almond and a young unripe nectarine, you will find that they resemble one another very closely. But as they ripen the outer coat of the nectarine grows juicier, while that of the almond grows stringier and coarser, till at last the one becomes what we commonly call a fruit, while the other becomes what we commonly call a nut. Here, again, the reason for the change is not difficult to divine. Some seeds succeed best by making themselves attractive and trusting to birds for their dispersion; others succeed best by adopting the tactics of concealment, by dressing themselves in green when on the tree, and in brown when on the ground, and by seeking rather to evade than to invite the attention of the animal world. Those seed vessels which aim at the first plan we know as fruits; those which aim rather at the second we know as nuts. The almond is just a nectarine which has gone back to the nut-producing habit. The cases are nearly analogous to those of the strawberry and the potentilla, only the strawberry is a fruit developed from a dry seed, whereas the almond is a dry seed developed from a fruit. To some extent this may be regarded as a case of retrogressive evolution or degeneration.
The second great divergent branch of the rose family — that of the pears and apples — has proceeded towards much the same end as the plums, but in a strikingly different manner. The apple kind have grown into trees, and have produced fruits. Instead, however, of the seed vessel itself becoming soft and succulent, the calyx or outer flower covering of the petals has covered up the carpels or young seed vessels even in the blossom, and has then swollen out into a sort of stalk-like fruit. The case, indeed, is again not unlike that of the strawberry, only that here the stalk has enlarged outward round the flower and inclosed the seeds, instead of simply swelling into a boss and embedding them. In the hip of the true roses we get some foreshadowing of this plan, except that in the roses the seeds still remained separate and free inside the swollen stalk, whereas in the pear and apple the entire fruit grows into a single solid mass. Here also, as before, we can trace a gradual development from the bushy to the tree-like form.
Fig. 47. — Vertical section of Apple-blossom.
The common hawthorn of our hedges shows us, perhaps, the simplest stage in the evolution of the apple tribe. It grows only into a tall bush, not unlike that of the blackthorn, and similarly armed with stout spines, which are really short sharp branches, not mere prickly hairs, as in the case of the brambles. Occasionally, however, some of the hawthorns develop into real trees, with a single stumpy trunk, though they never grow to more than mere small spreading specimens of the arboreal type, quite unlike the very tall and stately pear-tree. The flowers of the hawthorn — may-blossom, as we generally call them — are still essentially of the rose type; but, instead of having a single embryo seed and simple fruit in the centre, they have a compound fruit, inclosing many seeds, and all embedded in the thick fleshy calyx or flower-cup. As the haw ripens the flower-cup outside grows redder and juicier, and the seed pieces at the same time become hard and bony. For it is a general principle of all edible fruits that, while they are young and the seeds are unripe, they remain green and sour, because then they could only be losers if eaten by birds; but as the seeds ripen and become fit to germinate, the pulp grows soft and sweet, and the skin assumes its bright hue, because then the birds will be of service to it by diffusing the mature seeds. How largely birds assist in thus dispersing plants has very lately been proved in Australia, where a new and troublesome weed has rapidly overrun the whole country, because the fruit-eaters are very fond of it, and scatter its seeds broadcast over the length and breadth of the land.
The common medlar is nothing more than a hawthorn with a very big overgrown haw. In the wild state it bristles with hard thorns, which are wanting to the cultivated form, and its flower almost exactly resembles that of the may. The fruit, however, only becomes edible after it begins to decay, and the bony covering of the seeds is remarkably hard. It seems probable that the medlar, originally a native of southern Europe, is largely dispersed, not by birds, but by mice, rats, and other small quadrupeds. The colour is not particularly attractive, nor is the fruit particularly tempting while it remains upon the bush; but when it falls upon the ground and begins to rot, it may easily be eaten by rodents or pigs, and thus doubtless it procures the dispersion of its seeds under conditions highly favourable to their proper growth and success in life.
The little Siberian crabs, largely cultivated for their fruit in America, and sometimes found in English shrubberies as well, give us one of the earliest and simplest forms of the real apple group. In some respects, indeed, the apples are even simpler than the hawthorn, because their seeds or pips are not inclosed in bony cases, but only in those rather tough leathery coverings which form what we call the core. The haw of the hawthorn may be regarded as a very small crab-apple, in which the walls of the seed cells have become very hard and stony; or the crab may be regarded as a rather large haw, in which the cell walls still remain only thinly cartilaginous. The flowers of all the group are practically identical, except in size, and the only real difference of structure between them is in the degree of hardness attained by the seed covers. The crabs, the apples, and the pears, however, all grow into tallish trees, and so have no need for thorns or prickles, because they are not exposed to the attacks of herbivorous animals. Ordinary orchard apples are, of course, merely cultivated varieties of the common wild crabs. In shape the apple-tree is always spreading, like an arboreal hawthorn, only on a larger scale. The pear-tree differs from it in two or three small points, of which the chief are its taller and more pyramidal form, and the curious tapering outline of the fruit. Nevertheless, pear-trees may be found of every size and type, especially in the wild state, from a mere straggling bush, no bigger than a hawthorn, to a handsome towering trunk, not unlike an elm or an alder.
In the matter of fruits, the apple group are more advanced than the roses, but so far as regards the flower alone, viewed as an organ for attracting insects, many of the apple tribe are inferior to the true roses. Here again, however, we can trace a regular gradation from the small white blossoms of the may, through the larger blushing pink flowers of the apple, to the very expanded and brilliant crimson petals of that beautiful ornamental species of pear, the Pyrus japonica, so often trained on the sunny walls of cottages.
The quince is another form of apple very little removed from its congeners except in the fruit. More different in external appearance is the mountain-ash or rowan-tree, which few people would take at first sight for a rose at all. Nevertheless, its flowers exactly resemble apple-blossom, and its pretty red berries are only small crabs, dwarfed, no doubt, by its love for mountain heights and bleak windy situations, and clustered closely together into large drooping bundles. For the same reason, perhaps, its leaves have been split up into numerous small leaflets, which causes it to have been popularly regarded as a sort of ash. In the extreme north, the rowan shrinks to the condition of a stunted shrub; but in deep rich soils and warmer situations it rises into a pretty and graceful tree. The berries are eagerly eaten by birds, for whose attraction most probably they have developed their beautiful scarlet colour.
So far, all the members of the rose family with which we have dealt have exhibited a progressive advance upon the common simple type, whose embodiment we found in the little wayside potentillas. Their flowers, their fruits, their stems, their branches, have all shown a regular and steady improvement, a constant increase in adaptation to the visits of insects or birds, and to the necessities for defence and protection. I should be giving a false conception of evolution in the roses, however, if I did not briefly illustrate the opposite fact of retrogressive development or degeneration which is found in some members of the class; and though these members are therefore almost necessarily less familiar to us, because their flowers and fruits are inconspicuous, while their stems are for the most part mere trailing creepers, I must find room to say a few words about two or three of the most noteworthy cases, in order to complete our hasty review of the commonest rosaceous tribes. For, as we all know, development is not always all upward. Among plants and animals there are usually some which fall behind in the race, and which manage nevertheless to eke out a livelihood for themselves in some less honourable and distinguished position than their ancestors. About these black sheep of the rose family I must finally say a few words.
In order to get at them, we must go back once more to that simple central group of roses which includes the potentillas and the strawberry. These plants, as we saw, are mostly small trailers or creepers among grass or on banks; and they have little yellow or white blossoms, fertilised by the aid of insects. In most cases their flowers, though small, are distinct enough to attract attention in solitary arrangement. There are some species of this group, however, in which the flowers have become very much dwarfed, so that by themselves they would be quite too tiny to allure the eyes of bees or butterflies. This is the case among the meadow-sweets, to which branch also the spiræas of our gardens and conservatories belong. Our common English meadow-sweet has close trusses of numerous small whitish or cream-coloured flowers, thickly clustered together in dense bunches at the end of the stems; and in this way, as well as by their powerful perfume, the tiny blossoms, too minute to attract attention separately, are able to secure the desired attentions of any passing insect. In their case, as elsewhere, union is strength. The foreign spiræas cultivated in our hothouses have even smaller separate flowers, but gathered into pretty, spiky antler-like branches, which contrast admirably with the dark green of the foliage, and so attain the requisite degree of conspicuousness. This habit of clustering the blossoms which are individually dwarfed and stunted may be looked upon as the first stage of degradation in the roses. The seeds of the meadow-sweet are very minute, dry, and inedible. They show no special adaptation to any particular mode of advanced dispersion, but trust merely to chance as they drop from the dry capsule upon the ground beneath.
Fig. 48. — Single flower of Salad Burnet, male and female.
A far deeper stage of degradation is exhibited by the little salad-burnet of our meadows, which has lost the bright petals of its flowers altogether, and has taken to the wasteful and degenerate habit of fertilisation by means of the wind. We can understand the salad-burnet better if we look first at common agrimony, another little field weed about a foot high, with which most country people are familiar; for, though agrimony is not itself an example of degradation, its arrangement leads us on gradually to the lower types. It has a number of small yellow flowers like those of the cinquefoil; only, instead of standing singly on separate flower stalks, they are all arranged together on a common terminal spike, in the same way as in a hyacinth or a gladiolus. Now, agrimony is fertilised by insects, and therefore, like most other small field roses, it has conspicuous yellow petals to attract its winged allies. But the salad-burnet, starting from a somewhat similar form, has undergone a good deal of degradation in adapting itself to wind-fertilisation. It has a long spike of flowers, like the agrimony; but these flowers are very small, and are closely crowded together into a sort of little mop-head at the end of the stem. They have lost their petals, because these were no longer needed to allure bees or butterflies, and they retain only the green calyx or flower-cup, so that the whole spike looks merely a bit of greenish vegetation, and would never be taken for a blossoming head by any save a botanical eye. The stamens hang out on long thread-like stems from the cup, so that the wind may catch the pollen and waft it to a neighbouring head; while the pistils which it is to fertilise have their sensitive surface divided into numerous little plumes or brushes, so as readily to catch any stray pollen grain which may happen to pass their way. Moreover, in each head, all the upper flowers have pistils and embryo seed vessels only, without any stamens; while all the lower flowers have stamens and pollen bags only, without any pistils. This sort of division of labour, together with the same arrangement of seed-bearing blossoms above and pollen-bearing blossoms below, is very common among wind-fertilised plants, and for a very good reason. If the stamens and pistils were inclosed in a single flower they would fertilise themselves, and so lose all the benefit which plants derive from a cross, with its consequent infusion of fresh blood. If, again, the stamens were above and the pistils below, the pollen from the stamens would fall upon and impregnate the pistils, thus fertilising each blossom from others on the same plant — a plan which is hardly better than that of self-fertilisation. But when the stamens are below and the pistils above, then each flower must necessarily be fertilised by pollen from another plant, which ensures in the highest degree the benefits to be derived from a cross.
Thus we see that the salad-burnet has adapted itself perfectly to its new mode of life. Yet that adaptation is itself of the nature of a degradation, because it is a lapse from a higher to a lower grade of organisation — it is like a civilised man taking to a Robinson Crusoe existence, and dressing in fresh skins. Indeed, so largely has the salad-burnet lost the distinctive features of its relatives, the true roses, that no one but a skilled botanist would ever have guessed it to be a rose at all. In outer appearance it is much more like the little flat grassy plantains which grow as weeds by every roadside; and it is only a minute consideration of its structure and analogies which can lead us to recognise it as really and essentially a very degenerate and inconspicuous rose. Yet its ancestors must once have been true roses, for all that, with coloured petals and all the rosaceous characteristics, since it still retains many traces of its old habits even in its modern degraded form.
Fig. 49. — Flower of Stanch-Wound or Great Burnet.
We have in England another common weed, very like the salad-burnet, and popularly known as stanch-wound, or great-burnet, whose history is quite as interesting as that of its neighbour. The stanch-wound is really a salad-burnet which has again lost its habit of depending upon the wind for fertilisation, and has reverted to the earlier insect-attracting tactics of the race. As it had already lost its petals, however, it could not easily replace them, so it has coloured its calyx or flower-cup instead, which answers exactly the same purpose. In other words, having no petals, it has been obliged to pour the purple pigment with which it allures its butterfly friends into the part answering to the green covering of the salad-burnet. It has a head of small coloured blossoms, extremely like those of the sister species in many respects, only purple instead of green. Moreover, to suit its new habits, it has its cup much more tubular than that of the salad-burnet; its stamens do not hang out to the wind, but are inclosed within the tube; and the pistil has its sensitive surface shortened into a little sticky knob instead of being split up into a number of long fringes or plumes. All these peculiarities of course depend upon its return from the new and bad habit of wind-fertilisation to the older and more economical plan of getting the pollen carried from head to head by bees or butterflies. The two flowers grow also exactly where we should expect them to do. The salad-burnet loves dry and wind-swept pastures or rocky hill-sides, where it has free elbow-room to shed its pollen to the breeze; the stanch-wound takes rather to moist and rich meadows, where many insects are always to be found flitting about from blossom to blossom of the honey-bearing daisies or the sweet-scented clover.
