The species are as follow:—
Annual Rough-Leaved Summer Rape. Law.
Turnip Rape. Brassica rapa.
Root fusiform, small, hard, and woody; radical leaves lyrate, vivid green, and without any appearance of the glaucous bloom for which the biennial sorts are so distinguished; the stem-leaves are slightly glaucous, smooth, or nearly so,—the lower ones cut on the borders, the upper entire; the seeds are small, and similar to those of the common field turnip, of which it seems to be either a variety, or the source from which the latter has been derived.
Common or Winter Rape. Law.
Cole-seed. Brassica napus.
Biennial; root long, tapering, hard, and woody, like that of the species before described. The leaves are smooth, thick, and fleshy, and of much the same form as those of the Annual Rough-leaved Summer Rape; this species, however, being readily distinguished, when young, by its uniformly smooth leaves. The seeds, also, are larger than those of the last-named species; but this is not to be relied upon as a distinguishing characteristic, as the size of the seeds, in this as in most other plants, is liable to be materially altered by the soil as well as by the previous culture of the seed-stock.
The seeds are sown in summer, and the crop ripens the following year. It is not adapted to the climate of the Northern States.
In England, the foregoing species are extensively cultivated both for forage and for seed; the latter being used to a limited extent for feeding birds, but chiefly for the production of rape-seed oil.
German Rape. Law.