RAPE (Lat. rapum or rapa, turnip), in botany.—Several forms of plants included in the genus Brassica are cultivated for the oil which is present in their ripe seeds. The one most extensively grown for this purpose is known as colza, rape or coleseed, in Germany as Raps (Brassica napus, var. oleifera): its seeds contain from 30 to 45% of oil. The leaves are glaucous and smooth like those of a swede turnip. For a seed-crop rape is sown in July or early August in order that the plants may be strong enough to pass the winter uninjured. The young plants are thinned out to a width of 6 or 8 in. apart, and afterwards kept clean by hoeing. The foliage may be eaten down by sheep early in autumn, without injuring it for the production of a crop of seed. In spring the horse and hand hoe must be used, and the previous application of 1 cwt. or 2 cwt. of guano will add to the productiveness of the crop. On good soil and in favourable seasons the yield sometimes reaches to 40 bushels per acre. The haulm and husks are either used for litter or burned, and the ashes spread upon the land. It makes good fuel for clay-burning. There is a “summer” variety of colza which is sown in April and ripens its seed in the same year. It does not yield so much oil as the “winter” kind, but it will grow on soil in poorer condition. Neither of these is much grown in Great Britain for the production of oil, but the “winter” variety is very extensively grown as green food for sheep. For this purpose it is generally sown at short intervals throughout the summer to provide a succession of fodder. It is peculiarly adapted for peaty soils, and is accordingly a favourite crop in the fen lands of England, and on recently reclaimed mosses and moors elsewhere. Its growth is greatly stimulated by the ashes resulting from the practice of paring and burning. Its highly nutritious leaves and stems are usually consumed by folding the sheep upon it where it grows, there is no green food upon which they fatten faster. Occasionally it is carried to the homestead, and used with other forage in carrying out the system of soiling cattle.
The wild form Brassica campestris, the wild coleseed, colza or kohlsaat, of the fields of England and many parts of Europe, is sometimes cultivated on the European continent for its seed, which, however, is inferior in value to rape as an oil-yielding product.
In addition to the previously mentioned rape, a variety of another species (or subspecies) of Brassica, namely, Brassica rapa, var. oleifera (Rübsen in Germany), is grown for its oil yielding seeds. The leaves in a young state are not glaucous, but sap-green in colour and rough, being very similar to those of the turnip, to which the plant is closely related. Both winter and summer varieties are grown; they are rarely cultivated in Britain. The oil is similar to that in the true colza seeds but the plants do not yield so much per acre as the latter: they are, however, hardier and more adapted for cultivation on poor sandy soils.