TURNIP (Brassica Rape) a hardy biennial, which has been cultivated from a remote period for its fleshy roots. The tender growing tops are also used in spring as a green vegetable. The so-called "root" is formed by the thickening of the primary root of the seedling together with the base of the young stem (hypo cotyl) immediately above it. The great mass of the "root" con sists of soft "wood" developed internally by the cambium layer and composed mainly of thin-walled, unlignified, wood-paren chyma. The stem remains short during the first year, the leaves forming a rosette-like bunch at the top of the "bulb"; they are grass-green and bear rough hairs. In the second season the bud in the centre of the rosette forms a strong erect branched stem bearing somewhat glaucous smooth leaves. The stem and branches end in corymbose racemes of small, bright yellow flowers, which are succeeded by smooth, elongated, short-beaked pods.
The turnip probably originated in Europe or western Asia and by cultivation has spread throughout the temperate zone.
The varieties of turnip are classified according to their shape as (I) long varieties, with a root three or more times as long as broad; (2) tankard or spindle-shaped varieties, with a root about twice as long as broad; (3) round or globe varieties with an almost spherical root; (4) flat varieties with a root broader than long; there are also many intermediate forms. Turnips are also grouped according to the colour of the upper part of the root which comes above ground, and according to the colour of the flesh, which is white or yellow. The yellow-fleshed varieties, which are not hybrids between the turnip and swede, are more robust, of slower growth and superior feeding value to the white fleshed turnips, and are less injured by frost.
The swede-turnips, Brassica Napo-brassica and B. Rutabaga differ from the turnip proper in having the first foliage-leaves glaucous, not grass-green, in colour, and the later leaves smooth and glaucous; the root bears a distinct neck with well-marked leaf-scars, the flesh is white or yellow, firmer and more nutritious, and the roots keep much better during winter. The white-fleshed
forms (B. Napo-brassica) have a rough, green skin, firm white flesh and are of irregular form. The flowers are of a bright canary colour. The yellow-fleshed swede-turnips have a firm yellow flesh, a smooth skin of a green, purple or bronze colour. The flowers are buff yellow or pale orange.
Extensive British cultivation of turnips as a forage crop for sheep and cattle was first noticed in Suffolk about 1724; by the middle of the same century the crop had won an important position in the husbandry of Norfolk. In 1733 Tull had demonstrated the advantages of drilling and hoeing, but the crop continued to be grown broadcast until after the modern system had established itself in Border farming about 175o.
The adoption of turnip husbandry revolutionized British farm ing. It facilitated winter feeding of stock, the conversion of straw into yard manure for the improvement of the soil, and the recla mation of light and medium soils, which had previously been un productive under a system that depended on bare fallowing as the means of restoring fertility and freedom from weeds. The acre age of turnips increased with the gradual spread of rotation hus bandry, the enclosure of commons and the division of open fields into compact holdings. The increase continued during the third quarter of the 19th century, in the period of high farming and intensive corn and meat production; but after the commencement of the depression which followed, the acreage began an annual decline which has since been almost regular and continuous.
Turnip husbandry is still extensively practised in light-land arable districts that are not well adapted for dairying or other form of pastoral farming. Large areas of turnips are mainly associated with barley and sheep, but in some districts the crop is consumed wholly or partly by cattle.