Fig. 22.—Ripe fruit and detached seed of a Rose. show the nuts. The leaves are pinnate, consisting of two or more pairs of leaflets, and ending with an odd one. The leaves are furnished with very large stipules (see fig. 20 e); and the stems have numerous prickles (f), which differ from thorns in being articulated, that is, they may be taken off without tearing the bark of the stem on which they grow, only leaving the scar or mark, shown at g. The leaves of the sweet briar are full of small glands or cells filled with fragrant oil, which may be distinctly seen in the shape of little white dots, when held up to the light; and this is the reason of their delightful perfume. When the leaf is rubbed between the fingers, the thin skin that covers the cells is broken, and the oil being permitted to escape, the fragrance is increased. There are only two genera in this tribe, viz. Rosa and Lowea, the latter containing only what was formerly called Rosa berberifolia, and which has been thought worthy of being made into a separate genus principally on account of its having simple leaves without stipules, and branched prickles.
TRIBE II.—POTENTILLEÆ OR DRYADEÆ.
The plants belonging to this tribe agree more or less in the construction of their flowers with the well-known showy plants called Potentilla, but my readers will probably be surprised to hear that the raspberry and the strawberry are included among them. If, however, they compare the flower of the Potentilla with that of the strawberry, they will find them very much alike. In both there is a calyx of ten sepals, and a cup-shaped corolla of five petals; and in both the stamens form a ring round an elevated receptacle, on which are placed numerous carpels. Here, however, the resemblance ceases, for as the seeds of Potentilla ripen, the receptacle withers up in proportion to the swelling of the carpels, till it becomes hidden by them; while in the strawberry the receptacle becomes gradually more and more dilated, swelling out and separating the bony carpels still farther and farther from each other, till at last it forms what we call the ripe fruit. I have already had several times occasion to mention the receptacle, which though seldom seen, or at least noticed, by persons who are not botanists, is a most important part of the flower, and one that assumes a greater variety of form than any other. Sometimes, as we have seen in several of the Ranunculaceæ and Leguminosæ, it is a mere disk or flat substance serving as a foundation to hold together the other parts of the flower; and at other times we have found it drawn out into a thin membrane and divided into a kind of leaves, as it is among the carpels of the tree-peony; but in no plants that I have yet had occasion to describe does it assume such strange forms as in Rosaceæ.
The flower of the strawberry (Fragaria vesca) has a green calyx of ten sepals; five of which are much smaller than the others, and grow a little behind them, the large and small ones occurring alternately. The corolla is cup-shaped, and in five equal petals; the stamens are numerous and arranged in a crowded ring round the carpels, which are placed on a somewhat raised receptacle. The carpels or nuts resemble those of the rose, but they have no hairy covering, and indeed look hard and shining on the surface of the distended receptacle, or polyphore as it is called in its metamorphosed state. The carpels when ripe do not open to discharge the seed, and consequently as they are sown with the seeds, the young plants are a long time before they appear. The strawberry has what is called ternate leaves, that is, leaves consisting of three leaflets; with large membranous stipules. The calyx is persistent, that is, it remains on till the fruit is ripe.
The Raspberry (Rubus Idæus) differs widely from the strawberry in many particulars, notwithstanding their being included not only in the
Fig. 23.—Flowers and Fruit of the Raspberry. same natural order, but in the same tribe. The calyx has only five sepals (a in figure 23); and though the corolla has five petals (b), they do not form a cup-shaped flower. In the centre are the carpels, the form of which is shown of the natural size at c, and magnified at d, the latter showing that each has a separate style and stigma. As the raspberry advances, the petals drop, and the receptacle becomes elevated into what is called a torus, as shown of the natural size at e; bearing the carpels upon it, which gradually swell out and soften, till each becomes a little pulpy fruit, full of juice, and having the stone or seed in the centre. While this change is taking place, the stamens gradually wither and fall off, and the stigmas disappear, the style shrivelling up to the appearance of a hair; the pulpy carpels have also become so pressed against each other, as to adhere together, and the whole, with the persistent calyx, now assumes the appearance shown at f. As soon as the carpels become ripe they cease to adhere to the torus, and they may be pulled off and eaten (the torus, or core as it is called, being thrown away): each carpel will be found to inclose a very hard seed or stone, as shown at g. If the Raspberry, instead of being gathered, be suffered to remain on the stalk, the juicy carpels dry up, and fall with the seed inclosed. The stems of the Raspberry are biennial, that is, they do not bear till they are two years old, after which they die; but the roots are perennial, and they are always sending up fresh suckers, so that the same plants will bear for many years in succession, though not on the same stems. The stems are generally erect, and prickly like the rose; and the leaves on the bearing stems have three leaflets, while those on the barren stems have five; and in both cases the leaflets are covered with white down on the under side. All the different kinds of Bramble, such as the Dewberry, Blackberry, &c., agree with the Raspberry in the construction of their fruit, though they differ in the number of their leaflets, the size and colour of their flowers, and other minor particulars.
Several other genera belong to this tribe, among which may be mentioned Geum Avens, or Herb Bennet, the carpels of which have each a hooked style; Sieversia separated from Geum, because the carpels end in a straight feathery awn; and Tormentilla, the flowers of which bear a general resemblance to those of Potentilla, but which have an eight-parted calyx; a corolla of four petals; sixteen stamens, and dry wrinkled carpels on a depressed receptacle. All these genera my readers will find it interesting to procure flowers of, in order to compare them with each other. This and the preceding tribe are considered by some modern botanists to form the order Rosaceæ; the other tribes being formed into separate orders.