306 FIELD CROPS FOR THE COTTON-BELT 



following different stages in the evolution of. wheat: (1) 

 ^gilops ovata, a small annual grass of southern Europe, 

 having but one grain in each head; (2) the improved and 

 better developed form of this same species; (3) Triticum 

 spelia, the cultivated spelt of Europe; (4) Triticum poloni- 

 cum, Polish wheat; (5) Triticum sativum, common wheat. 



374. Botanical classification. — Following is shown 

 the botanical classification of common wheat: Order — 

 Gramineae; tribe — Hordese; genus — '■ Triticum; species — 

 sativum; subspecies — vulgare. 



Each member of the tribe (Hordese) to which wheat, rye, 

 and barley belong produces its inflorescence in the form of 

 a spike, rather than in a panicle as do the members of the 

 tribe (Avenae) to which oats belong. Other cultivated 

 grasses' belonging to the same tribe as wheat are perennial 

 rye-grass (Lolium perenne), and ItaUan rye-grass {Lolium 

 italicum). Some troublesome weeds belonging to this 

 tribe are darnel (Lolium temulentum), and couch-grass 

 (Agropyron repens). 



STRUCTURE AND COMPOSITION OF WHEAT 



375. Roots. — In germinating, the wheat grain throws 

 out a whorl of 3 to 8 temporary roots. The first of these 

 to appear is called the radicle. Immediately following 

 the appearance of the temporary roots the stalk begins 

 to develop. At each underground joint a whorl of per- 

 manent roots is thrown out. The distance between the 

 temporary roots and the joints at which the permanent 

 roots are borne will be governed primarily by the depth 

 of planting. The permanent roots usually occur about 

 one inch below the surface of the soil, irrespective of 

 the depth of planting. No tap-root is produced. The 

 roots are quite fibrous and tend to curve outward for a 



