When the flower first expands, the ovary, if cut open and examined, will be found to be divided into several cells, each containing two rows of ovules. As in the preceding genera, however, many of these ovules become abortive; and as the cells fill gradually with cellular pulp, the seeds become detached from the placenta, and buried in it. The seeds themselves are very interesting; they are covered with a thick wrinkled skin, and they show distinctly the hilum (_c_ in _fig._ 121), the chalaza (_d_) and the raphe or connecting cord between them, parts which are seldom to be distinguished in seeds with the naked eye. [Illustration: FIG. 122.—LEAF AND FRUIT OF THE ORANGE.] The leaves, calyx, and petals of the Orange, if held up to the light, appear covered with little dots. These dots are cells, covered with a transparent membrane, and filled with a kind of oil, which is exceedingly fragrant. The rind of the fruit is covered with similar cells, filled with a pungent oily liquid. The leaves are smooth and shining; and they are articulated; that is, they can be separated from the petiole or footstalk without lacerating them. In most of the species, the petioles are winged; that is, they are dilated into little leaves on each side (see _d_ in _fig._ 122). The different species vary chiefly in the number of stamens, the thickness of the rind, the shape of the fruit, and in the wings of the petioles. In the Citron these wings are wanting entirely, and instead of them there are spines in the axils of the leaves; there are generally forty stamens, and the rind of the fruit is very thick. In the sweet Lime, the petioles are slightly winged, and there are about thirty stamens; the fruit is small and round, with a slight protuberance at one end like that of the Lemon, and the pulp is sweet. In the Lemon the petioles are somewhat winged, the flowers have about thirty stamens; the fruit is oblong, with an acid pulp, and a thin rind. The Sweet Orange has winged petioles, about twenty stamens, and a fruit with a thin rind and sweet pulp; and the Seville Orange differs principally in having a thicker rind and bitter pulp. The China, St. Michael, and Malta Oranges, with many others, are all varieties of the Sweet Orange (_Citrus Aurantium_); and there are many other species, which I have not thought it necessary to describe.—All the species above-mentioned are natives of Asia, and most of them of China, but they have been so long cultivated in Europe and America, as to have become almost naturalised. ORDER XXXVIII.—HYPERICINEÆ.—THE HYPERICUM TRIBE.