_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.