ROOTS AND ROOT-HAIRS. 39 



ment of root-hairs. If the soil is too wet they 

 are not developed. 



These facts are of importance as correlated 

 with the ease or difficulty experienced by the 

 roots in obtaining water, and plants such as our 

 ordinary agricultural plants show this very dis- 

 tinctly. 



Although, as shown in the experiments with 

 wheat, the short roots in dry soil were more 

 densely covered with root-hairs than the much 

 longer roots in moderately moist soil, subsequent 

 closer investigation shows that the total quantity 

 and area of root-hairs is less in the former case 

 than in the latter. 



The greatest number of root-hairs are developed 

 on roots which are growing at their best : too 

 much moisture may prevent the formation of root- 

 hairs : too little may induce dense growths of 

 root-hairs locally, but the total number is reduced. 



Another set of events which exerts influence 

 on the development of root-hairs is the com- 

 position of the dilute solution water containing 

 dissolved salts which surrounds them in the soil. 



Thus, Schwarz found that when similar oat 

 and wheat plants were grown with their roots 

 in solutions of various salts, the results differed 

 as follows : 



Oats in a 15 per cent, solution of calcium 

 chloride developed no root-hairs, though they 

 formed in a 5 per cent, solution, and were very 

 numerous in a 0.5 per cent, solution, or in water 

 alone. In a 10 per cent, nutritive solution the 



