SORGHUMS 263 



drought and again growing with the advent of favorable 

 weather. On these accounts it is especially well adapted 

 to agriculture in* semi-arid regions. 



312. Root system. In Ten Eyck's studies at the Kan- 

 sas Experiment Station, the roots of kafir and of Folger 

 sorgo were found to extend to a depth of 3J feet, but at 

 that depth were less abundant than those of corn. Both 

 varieties, especially the kafir corn, produced an enormous 

 amount of roots in the upper 18 inches. The sorghums 

 therefore have a root system especially well adapted to use 

 shallow moisture promptly. 



In Russian investigations the roots of two varieties 

 of sorghum penetrated respectively 106 and 110 centi- 

 meters, while corn roots went to a depth of 113 centi- 

 meters and spread laterally to a greater extent than the 

 sorghum. 



The drought resistance of sorghums would therefore 

 seem not to be especially associated with the development 

 of the root system. 



313. Agricultural groups. No other cultivated crop 

 exhibits as great a diversity as does sorghum. Varieties 

 have been developed for three distinct purposes ; namely, 

 grain, sugar and broom-straw. All three of the groups 

 also . produce forage as a by-product. A satisfactory 

 classification of the very numerous forms of tropical Africa 

 is not at present possible, but very many of them have 

 been named by botanists. So far as the forms cultivated 

 in America are concerned, the classification into groups as 

 proposed by Ball is here adopted, adding another group, 

 however, to include Sudan-grass and Tunis-grass. 



* Stems slender, rarely exceeding 6 mm. in diameter ; leaves 

 relatively narrow, 12 to 30 mm. broad ; panicles loose ; spikelets 



