372 



CRUCIFER^ 



biennial plant grown extensively for its thick fleshy so-called 

 'roots,' which are produced during the first season of growth 

 and used as late summer, autumn and winter food for various 

 kinds of stock. 



Seed and Germination. — The seed is almost round, with a 

 reddish purple testa, and contains an embryo which resembles 

 that of white mustard in general form (Fig. 5). The seedling 

 possesses two smooth notched cotyledons and a hypocotyl and 

 root very distinct from each other. The first foliage-leaves are 



Fig. 118. — I. Longitudinal section of a turnip *root.' 2. Transverse section of the 

 same, d Bast and secondary cortex; c cambium-ring ; a degenerate wood, forming 

 main mass of the root ; r normal secondary root, originally produced when the primary 

 root was thin (almost all above this point is thickened hypocotyl} ; b old leaf-scars. 



grass-green in colour, roundish with irregularly serrate margins and 

 their surfaces have scattered hispid hairs upon them. 



Root and Hvpocotvl. — A single tap root generally exists 

 from which a number of thin secondary roots arise. The total 

 root-system, although fairly extensive, does not descend to any 

 great depth, but spreads horizontally in the upper layers of the soil. 



During the first year, both the hypocotyl and primary root 

 increase in length and thickness, the combined thickened 



