by Grant Allen
Perhaps the simplest and earliest type of the rose family now remaining in England is to be found in the little yellow potentillas which grow abundantly in ill-kept fields or by scrubby roadsides. The potentillas are less familiar to us than most others of the rose family, and therefore I am sorry that I am obliged to begin by introducing them first to my reader’s notice rather than some other and older acquaintance, like the pear or the hawthorn. But as they form the most central typical specimen of the rose tribe which we now possess in England, it is almost necessary to start our description with them, just as in tracing a family pedigree we must set out from the earliest recognisable ancestor, even though he may be far less eminent and less well-known than many of his later descendants. For to a form very much like the potentillas all the rose family trace their descent. The two best known species of potentilla are the goose-weed or silver-weed, and the cinquefoil. Both of them are low creeping herb-like weeds, with simple bright yellow blossoms about the size of a strawberry flower, having each five golden petals, and bearing a number of small dry brown seeds on a long green stalk. At first sight a casual observer would hardly take them for roses at all, but a closer view would show that they resemble in all essential particulars an old-fashioned single yellow rose in miniature. From some such small creeping plants as these all the roses are probably descended. Observe, I do not say that they are the direct offspring of the potentillas, but merely that they are the offspring of some very similar simple form. We ourselves do not derive our origin from the Icelanders; but the Icelanders keep closer than any other existing people to that primitive Teutonic and Scandinavian stock from which we and all the other people of northwestern Europe are descended. Just so, the roses do not necessarily derive their origin from the potentillas, but the potentillas keep closer than any other existing rose to that primitive rosaceous stock from which all the other members of the family are descended.
The strawberry is one of the more developed plants which has varied least from this early type represented by the cinquefoil and the silver-weed. There is, in fact, one common English potentilla, whose nature we have already considered, and which bears with village children the essentially correct and suggestive name of barren strawberry. This particular potentilla differs from most others of its class in having white petals instead of yellow ones, and in having three leaflets on each stalk instead of five or seven. When it is in flower only it is difficult at first sight to distinguish it from the strawberry blossom, though the petals are generally smaller, and the whole flower less widely opened. After blossoming, however, the green bed or receptacle on which the little seeds are seated does not swell out (as in the true strawberry) into a sweet, pulpy, red mass, but remains a mere dry stalk for the tiny bunch of small hard inedible nuts. The barren strawberry, indeed, as we saw in an earlier paper, is really an intermediate stage between the other potentillas and the true eatable strawberry; or, to put it more correctly, the eatable strawberry is a white-flowered potentilla which has acquired the habit of producing a sweet and bright-coloured fruit instead of a few small dry seeds. Since we have got to understand the rationale of this first and simplest transformation, we have now a clue by which we may interpret almost all the subsequent modifications of the rose family, and I must therefore be permitted here briefly to recapitulate the chief points we have already proved in this matter.
The true strawberry, we saw, resembles the barren strawberry in every particular except in its fruit. It is a mere slightly divergent variety of that particular species of potentilla, though the great importance of the variety from man’s practical point of view causes us to give it a separate name, and has even wrongly induced botanists to place it in a separate genus all by itself. In reality, however, the peculiarity of the fruit is an extremely slight one, very easily brought about. In all other points — in its root, its leaf, its stem, its flower, nay, even its silky hairs — the strawberry all but exactly reproduces the white potentilla. It is nothing more than one of these potentillas with a slight diversity in the way it forms its fruit. To account, therefore, for the strawberry we had first to account for the white potentilla from which it springs.
The white potentilla, or barren strawberry, you will remember, is itself a slightly divergent form of the yellow potentillas, such as the cinquefoil. From these it differs in three chief particulars. In the first place, it does not creep, but stands erect; this is due to its mode of life on banks or in open woods, not among grass and meadows as is the case with the straggling cinquefoil. In the second place, it has three leaflets on each stalk instead of five, and this is a slight variation of a sort liable to turn up at any time in any plant, as the number of leaflets is very seldom quite constant. In the third place, it has white petals instead of yellow ones, and this is the most important difference of any. All flowers with bright and conspicuous petals we know are fertilised by insects, which visit them in search of honey or pollen, and the use of the coloured petals is, in fact, to attract the insects and to induce them to fertilise the seeds. Now, yellow seems to have been the original colour of the petals in almost all (if not absolutely in all) families of flowers; and the greater number of potentillas are still yellow. But different flowers are visited and fertilised by different insects, and as some insects like one colour and some another, many blossoms have acquired white or pink or purple petals in the place of yellow ones, to suit the particular taste of their insect friends. In tracing the upward course of development in the roses, we shall see that they follow the ordinary law of progressive chromatic changes: the simpler types are yellow; the somewhat higher ones are white; the next pink; and the highest in this particular family are red; for no rose has yet attained to the final stage of all, which is blue. The colours of petals are always liable to vary, as we all see in our gardens, where florists can produce at will almost any shade or tint that they choose; and when wild flowers happen to vary in this way, they often get visited by some fresh kind of insect which fertilises their seeds better than the old ones did, and so in time they set up a new variety or a new species. Two of our English potentillas have thus acquired white flowers to suit their proper flies, while one boggy species has developed purple petals to meet the æsthetic requirements of the marshland insects. No doubt the white blossoms of the barren strawberry are thus due to some original ‘sport’ or accidental variation, which has been perpetuated and become a fixed habit of the plant because it gave it a better and surer chance of setting its seeds, and so of handing down its peculiarities to future generations.
And now, how did we find the true strawberry had developed from the three-leaved white potentilla? Here the birds came in to play their part, as the bees and flies had done in producing the white blossom. Birds are largely dependent upon fruits and seeds for their livelihood, and so far as they are concerned it does not matter much to them which they eat. But from the point of view of the plant it matters a great deal. For if a bird eats and digests a seed, then the seed can never grow up to be a young plant; and it has so far utterly failed of its true purpose. If, however, the fruit has a hard indigestible seed inside it (or, in the case of the strawberry, outside it), the plant is all the better for the fact, since the seed will not be destroyed by the bird, but will merely be dispersed by it, and so aided in attaining its proper growth. Thus, if certain potentillas happened ever to swell out their seed receptacle into a sweet pulpy mass, and if this mass happened to attract birds, the potentillas would gain an advantage by their new habit, and would therefore quickly develop into wild strawberries as we now get them. But the difference between the strawberry fruit and the potentilla fruit is to the last a very slight one. Both have a number of little dry seeds seated on a receptacle; only, in the strawberry the receptacle grows red and succulent, while in the potentilla it remains small and stalk-like. The red colour and sweet juice of the strawberry serve to attract the birds which aid in dispersing the seed, just as the white or yellow petals and the sweet honey of the potentilla blossoms serve t
o attract the insects which aid in fertilising the flowers. In this way all nature is one continual round of interaction and mutual dependence between the animal and vegetable worlds.
Fig. 44. — Fruit of Bramble.
Fig. 45. — Flower of Bramble.
The potentillas and the strawberry plant are all of them mere low creeping or skulking herbs, without woody stems or other permanent branches. But when we get to the development of the brambles or blackberry bushes, we arrive at a higher and more respectable division of the rose family. There are two or three intermediate forms, such as water-avens and herb-bennet — tall, branching, weedy-looking roadside plants — which help us to bridge over the gulf from the one type to the other. Indeed, even the strawberry and the cinquefoil have a short perennial, almost woody stock, close to the ground, from which the annual branches spring; and in some other English weeds of the rose family the branches themselves are much stiffer and woodier than in these creeping plants. But in the brambles, the trunk and boughs have become really woody, by the deposit of hard material in the cells which make up their substance. Still, even the brambles are yet at heart mere creepers like the cinquefoil. They do not grow erect and upright on their own stems: they trail and skulk and twine in and out among other and taller bushes than themselves. The leaves remain very much of the cinquefoil type; and altogether there is a good deal of the potentilla left in the brambles even now.
However, these woody climbers have certainly some fresh and more developed peculiarities of their own. They are all prickly shrubs, and the origin of their prickles is sufficiently simple. Even the potentillas have usually hairs on their stems; and these hairs serve to prevent the ants and other honey-thieving insects from running up the stalks and stealing the nectar intended for fertilising bees and butterflies. Similar hairs in the goose-grass grew, you will recollect, into the little clinging hooks of the stems and midribs. But in the brambles, hairs of the same sort have grown still thicker and stouter, side by side with the general growth in woodiness of the whole plant; so that they have at last developed into short thorns, which serve to protect the leaves and stem from herbivorous animals. As a rule, the bushes and weeds which grow in waste places are very apt to be protected in some such fashion, as we see in the case of gorse, nettles, blackthorn, holly, thistles, and other plants; but the particular nature of the protection varies much from plant to plant. In the brambles it takes the form of stiff prickly hairs; in the nettles, of stinging hairs; in the gorse, of pointed leaves; and in the thorn-bushes of short, sharp, barren branches.
Another peculiarity of the bramble group is their larger white flowers and their curious granulated fruit. The flowers, of course, are larger and whiter in order to secure the visits of their proper fertilising insects; the fruits are sweet and coloured in order to attract the hedgerow birds. Observe, too, that the flowers being higher in type than those of the strawberry, are often tinged with pink: here we get the first upward step in the direction of the true roses. The nature of the fruit in the raspberry, the blackberry, and the dewberry, again, is quite different from that of the strawberry. Here, instead of the receptacle swelling out and growing red and juicy, it is the outer coat of the separate little seeds themselves that forms the eatable part; while the receptacle remains white and inedible, being the ‘hull’ or stem which we pick out from the hollow thimble-like fruit in the raspberry. Each little nut, which in the strawberry was quite hard and brown, is here covered with a juicy black or red pulp, inside which lies the stony real seed; so that a blackberry looks like a whole collection of tiny separate fruits, run together into a single head. Moreover, there are other minor differences in the berries themselves, even within the bramble group; for while the raspberry and cloudberry are red, to suit one set of birds, the blackberry and dewberry are bluish black, to suit another set; and while the little grains hold together as a cup in the raspberry, but separate from the hull, they cling to the hull in the other kinds. Nevertheless, in leaves, flower, and fruit there is a very close fundamental agreement among all the bramble kind and the potentillas. Thus we may say that the brambles form a small minor branch of the rose family, which has first acquired a woody habit and a succulent fruit, and has then split up once more into several smaller but closely allied groups, such as the blackberries, the raspberries, the dewberries, and the stony brambles.
Fig. 46. — Vertical section of a Dog-rose.
The true roses, represented in England by the dog-rose and sweet-briar, show us a somewhat different development from the original type. They, too, have grown into tall bushes, less scrambling and more erect than the brambles. They have leaves of somewhat the same sort, and prickles which are similarly produced by the hardening of sharp hairs upon the stem. But their flowers and fruit are slightly more specialised — more altered, that is to say, for a particular purpose from the primitive plan. In the first place, the flowers, though still the same in general arrangement, with five petals and many stamens and carpels (or fruit-pieces), have varied a good deal in detail. The petals are here much larger, and they have advanced to the stage of a brilliant pink; while the blossoms are also sweet-scented. These peculiarities of course serve to attract the bees and other large fertilising insects, which thus carry pollen from head to head, and aid in setting the seeds much more securely than the little pilfering flies. Moreover, in all the roses, the outer green cup which covers the blossom in the bud has grown up around the little seeds or fruit-pieces, so that instead of a ball turned outward, as in the strawberry and raspberry, you get, as it were, a bottle turned inward, with the seeds on the inner side. After flowering, as the fruit ripens, this outer cup grows round and red, forming the hip or fruit-case, inside which are to be found the separate little hairy seeds. Birds eat this dry berry, though we do not, and thus aid in dispersing the species. But though they digest the soft red outer pulp, formed by the swollen stalk, they cannot digest the hairy seed, so the plant attains its prime object of getting them duly scattered. The true roses, then, are another branch of the original potentilla stock, which have acquired a bushy mode of growth, with a fruit differing in construction from that of the brambles. Our English kinds are merely pink; the more developed exotics are often scarlet and crimson.
We have altogether some five true wild roses in Britain. The commonest is the dog-rose, which everybody knows well; and next comes the almost equally familiar sweet-briar, with its delicately scented glandular leaves. The burnet-rose is the parent of our cultivated Scotch roses, and the two other native kinds are comparatively rare. Double garden roses are produced from the single five-petalled wild varieties by making the stamens (which are the organs for manufacturing pollen) turn into bright-coloured petals. There is always more or less of a tendency for stamens thus to alter their character; but in a wild state it never comes to any good, because such plants can never set seed, for want of pollen, and so die out in a single generation. Our gardeners, however, carefully select these distorted individuals, and so at length produce the large, handsome, barren flowers with which we are so familiar. The cabbage and moss roses are monstrous forms thus bred from the common wild French roses of the Mediterranean region; the China roses are cultivated abortions from an Asiatic species; and most of the other garden varieties are artificial crosses between these or various other kinds, obtained by fertilising the seed vessels of one bush with pollen taken from the blossoms of another of a different sort. To a botanical eye, double flowers, however large and fine, are never really beautiful, because they lack the order and symmetry which appear so conspicuously in the five petals, the clustered stamens, and the regular stigmas of the natural form.
From the great central division of the rose family, thus represented by the potentillas, the strawberry, the brambles, and the true roses, two main younger branches have diverged much more widely in different directions. As often happens, these junior offshoots have outstripped and surpassed the elder stock in many points of structure and function. The first of the two branches in
question is that of the plum-tribe; the second is that of the pears and apples. Each presents us with some new and important modifications of the family traits.
Of the plum tribe, our most familiar English examples, wild or cultivated, are the sloe or blackthorn, with its descendant the garden plum; as well as the cherry, the apricot, the peach, the nectarine, and the almond. All these plants differ more or less conspicuously from the members of the central group which we have so far been examining in their tree-like size and larger trunks. But they also differ in another important point: each flower contains only one seed instead of many, and this seed is inclosed in a hard bony covering, which causes the whole plum tribe (except only the almond, of which more anon) to be popularly included under the common title of ‘stone-fruits.’ In most cases, too, the single seed is further coated with a soft, sweet, succulent pulp, making the whole into an edible fruit. What, now, is the reason for this change? What advantage did the plant derive from this departure from the ordinary type of rose-flower and rose-fruit? To answer this question we must look at one particular instance in detail, and we cannot do better than take that well-known fruit, the cherry, as our prime example of the whole class.
The cherry, like the strawberry, is an eatable fruit. But while in the strawberry we saw that the pulpy part consisted of the swollen stalk or receptacle, in which several small dry seeds were loosely embedded, with the cherry the pulpy part consists of the outer coat of the fruit or seed vessel itself, which has grown soft and juicy instead of remaining hard and dry. In this respect the cherry resembles a single grain from a raspberry; but from the raspberry, again, it differs in the fact that each flower produces only a single solitary one-seeded fruit, instead of producing a number of little fruits, all arranged together in a sort of thimble. In the raspberry flower, when blossoming, you will find in the centre several separate carpels or fruit-pieces; in the cherry you will find only one. The cherry, in fact, may (so far as its fruit is concerned) be likened to a raspberry in which all the carpels or fruit-pieces except one have become aborted. And the reason for the change is simply this: cherry bushes (for in a wild state they are hardly trees) are longer-lived plants than the bramble kind, and bear many more blossoms on each bush. Hence one seed to every blossom is quite as many as they require to keep up the numbers of the species. Moreover their large and attractive fruits are much more likely to get eaten and so dispersed by birds than the smaller and less succulent berries of the brambles. Furthermore, the cherry has a harder stone around each seed, which is thus more effectually protected against being digested, and the seed itself consists of a comparatively big kernel, richly stored with food-stuffs for the young plant, which thus starts relatively well equipped in the battle of life. For all these reasons the cherries are better off than the brambles, and therefore they can afford to produce fewer seeds to each flower, as well as to make the coverings of these seeds larger and more attractive to birds. Originally, indeed, the cherry had two kernels in each stone, and to this day it retains two little embryo kernels in the blossom, one of which is usually abortive afterwards (though even now you may sometimes find two, as in philipœna almonds); but one seed being ordinarily quite sufficient for all practical purposes, the second one has long since disappeared in the vast majority of cases.
