278 Irrigation and Drainage 



produced. When such conditions as those represented 

 in 3 and 4 are set up, marked wilting must result and 

 growth be brought nearly or quite to a standstill. 



It is not possible to state with certainty what 

 strength of salt solution existed in the soil moisture in 

 the cases cited above, but an approximate estimate 

 may be made. Hilgard's analyses show, in the case 

 of the sample from where barley would not grow, 

 that the soluble alkalies amounted to 2.44 pounds per 

 100 pounds of soil. If these salts were all in solution 

 in the soil -water, and if the soil -water amounted to 

 30 per cent of the dry weight of the soil, then the 

 salts in solution would have a strength of 8.13 per 

 cent. But if only 15 per cent of moisture existed in 

 the soil, as might easily have been the case, and all 

 the salts were in solution, then its strength would 

 have been double that above, and much stronger than 

 DeVries' most severe trial. It does not appear im- 

 probable, therefore, that even were there no poisonous 

 effect exerted upon the barley by the salts in the soil, 

 the plants could not have grown, on account of the wilt- 

 ing which would have resulted from the presence of 

 too strong a salt solution outside the cell walls of the 

 root -hairs in the soil. 



COMPOSITION OF ALKALI SALTS 



To show the character of the salts which accumu- 

 late in the manner under consideration, we have 

 computed the mean composition from a number of 

 analyses as given by Hilgard, and the results are 

 stated in the table which follows : 



