TURNIP, Brassica campestris, var. Rapa, a hardy biennial, found in cornfields in various parts of England. It 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 (hypocotyl) immediately above it. The great mass of the " root " consists of soft " wood " developed internally by the cambium layer and composed mainly of thin-walled, unlignified, wood-parenchyma. 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 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, many of which are probably hybrids between the turnip and swede, are mote robust, of slower growth and superior feeding value to the white-fleshed turnips, and are less injured by frost. The swede-turnip, Brassica campestris, var. Napo-brassica, differs 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 yellow or reddish-orange, firmer and more nutritious, and the roots keep much better during winter. The flowers are larger and buff-yellow or pale orange in colour and the seeds are usually larger and darker than in the turnip.
Turnips should be grown in a rich friable sandy loam, such as will produce medium-sized roots without much aid from the manure heap, and are better flavoured if grown in fresh soil. In light dry soils well decomposed hotbed or farmyard manure is the best that can be used, but in soils containing an excess of organic matter, bone dust, superphosphate of lime, wood-ashes or guano, mixed with light soil, and laid in the drills before sowing the seed, are beneficial by stimulating the young plants to get quickly into rough leaf, and thus to grow out of reach of the so-called turnip fly or turnip flea (Phyllotreta). To get rid of this pest, it has been found beneficial to dust the plants with quicklime, and also to draw over the young plants nets smeared with some sticky substance like treacle, by which large numbers will be caught and destroyed. It has been also recommended as a palliative to sow thick in order to allow for a percentage of loss from this and other causes, but this is inadvisable, as overcrowding is apt to render the plants weak. As a preventive, gas-lime may be scattered over the surface after the seed has been sown. Lime is also effective against the disease known as " finger and toe " (q.v.).
The first sowing should be made on a warm border, with the protection of a frame or matted hoops, in January or February; the second on a well-sheltered border in March, after which a sowing once a month will generally suffice. In May and June the plot should be in a cool moderately shaded position, lest the plants should suffer from drought. The principal autumn and winter sowings, which are the most important, should be made about the end ofjune in the northern districts, and in the beginning of July in warmer districts ; a small sowing may be made at the end of August to come in before the spring-sown crops are ready. If the weather is showery at the time of sowing, the seed speedily germinates, and the young plants should be kept growing quickly by watering with rain or pond water and by surface stirrings. The drills for the earliest sorts need not be more than 15 in. apart, and the plants may be left moderately thick in the row; the late crops should have at least 2 ft. between the rows, and be thinned to 12 in. in the row, a free circulation of air about them being very important in winter. As a provision against prolonged periods of severe weather it has been recommended to lay the finest roots in rows, covering them well with soil, and leaving intact the whole of the foliage. The very latest sown crops of half-grown roots will prolong the supply until the earliest spring-sown crops are fit for use.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)