24 



CIRCULAR NO. 109, BUREAU OP PLANT INDUSTRY. 



when the wilting coefficient had been reached in the least saline mix- 

 tures, the soil-moisture content (determined when it became evident 

 that the plants would make no further growth) was found to be 22.8 

 per cent. Since the initial water content of this soil was 23.7 per 

 cent and the initial moisture available for growth was 10.4 per cent 

 (Table II), the loss of water by transpiration in this glass amounted 

 to only 3.8 per cent of the total and 8.6 per cent of the available 

 moisture present at the outset. 



While the moisture content of all the soils was finally reduced in at 

 least one of the glasses to the wilting coefficient, tins happened much 

 more rapidly in the soils winch had a high electrical resistance (low 

 salt content) than in those which had a low electrical resistance (high 

 salt content). There was, on the whole, a remarkably close correla- 

 tion between the salt content of the soil and the length of time 

 required for the plants to reach a wilted condition. The relation is 

 expressed hi Table VI. 



Table VI. — Time required to exhaust in each soil mixture the water available for growth. 



Number 

 of glasses 

 in which 

 wilting 

 occurred. 



CONCLUSIONS. 



The results of this experiment make possible the following conclu- 

 sions : 



(1) The presence of an excess of soluble salts in a soil did not affect 

 the ability of young wheat plants to reduce ultimately the water con- 

 tent of that soil to the wilting coefficient, unless the quantity of salts 

 was sufficient to induce marked pathological symptoms in the plants. 



(2) The time required for the exhaustion of the water available for 

 growth increased steadily with increasing concentration of the soil 

 solution (Table VI). 



(3) The amount of growth made, so. long as the moisture content 

 of the soil remained well above the wilting coefficient, was deter- 

 mined by the concentration of the soil solution (Table IV). 



(4) The presence of alkali increased the water requirement of the 

 plants ; in other words, increased the quantity of water transpired in 



LCir. 109] 



