280 



PLANT PHYSIOLOGY 



revealed when a plant is dug up in the usual way. The greater 

 part of the most active fine rootlets are usually torn off in digging. 

 Rotmistroff, in Russia, and Weaver, in America, were the first 

 to give a correct idea of the real extent of the root system, when 

 all of its small branches remain intact. These authors have 

 shown that even in cereals, like oats and wheat, the root system 



■"■■7i.*frws^j»*Tr'^^f^-r* 



Fig. 81. — Amount of water evaporated during the summer by one maize plant 



{after Sinnott). 



is not confined to the tilled layer. It penetrates into the soil to 

 a depth of 1.5 to 2 m. and spreads extensively in all directions 

 (Fig. 82). The roots of alfalfa and other plants of dry habitats 

 penetrate considerably deeper. Even for small plants, the total 

 length of the roots with all their branches measures several 

 hundred meters. In larger plants, this length has to be measured 

 by kilometers. The absorbing surface of the roots is increased 

 several times by the development of root hairs. Such an 



