236 THE SMALL GRAINS 



ways in which lime is useful, however, that are not usually 

 recognized. Hilgard has often remarked upon the pres- 

 ence of lime in our prairie soils, and mentions the fol- 

 lowing ways in which it acts as a soil factor : "It 

 causes (a) a more rapid transformation of vegetable 

 matter into active humus, which manifests itself by a 

 dark or deep black tint of the soil, and (b) the retention 

 of such humus against the oxidizing influences of hot 

 climates, (c) Whether through the medium of this 

 humus, or in a more direct manner, it renders adequate 

 for profitable culture percentages of phosphoric acid and 

 potash so small that in the case of deficiency or absence 

 of lime the soil is practically sterile, (d) It tends to 

 secure the proper maintenance of the conditions of nitri- 

 fication whereby the inert nitrogen of the soil is rendered 

 available, (e) It exerts a most important physical action 

 in the flocculation and therefore tillability of the soil. 

 (/) In the same connection it tends to increase the ab- 

 sorption coefficients of soils for moisture and gases." 



249. The origin of prairies. Much has been written 

 on the origin of prairies without any agreement in con- 

 clusions. Various theories have been offered by Winchell, 

 Lesquereux, J. D. Whitney, and others in this country. 

 Russian investigators have given far more attention to 

 the subject than any others and agree upon the theory of 

 the presence of vegetation itself as the chief factor in 

 black soil formation, but modified and controlled to a 

 great extent by other factors such as temperature and 

 moisture. 1 However theories as to origin may differ, 



1 So persistent have been the activities of Russian investi- 

 gators of the botany and surface geology of the Chernozem that 

 a school of geo-botanists has arisen pursuing practically a dis- 

 tinct new science of geo-botany. The leaders were Ruprecht 



