igi6] SHULL— SOILS 19 



When the soil moisture reaches 6 per cent above air-dry, the 

 moisture intake by seeds indicates a force equivalent to 4M. NaCl 

 solution, which is estimated to exceed 130 atmospheres. At n 

 per cent above air-dry the holding power of the soil has fallen to 

 22.5 atmospheres approximately. 



In this manner, comparing the percentage intake from the soil 

 with that from the solutions, as given in table III, one may estimate 

 the surface force for any given moisture content of the soil, each 

 soil type, of course, having specific relations. If it were possible 

 to make absolutely accurate determinations for several points in 

 the curve of moisture intake by seeds, as related to the curve of 

 moisture increase in a particular soil, it would be a simple mathe- 

 matical problem to calculate the exact water-holding power of 

 the soil particles at any soil moisture content whatsoever for 

 that soil. 



2. The no. 2/0 sand. — By preliminary tests ranging from 17.5 

 per cent to 1 per cent of moisture it was found that there was no 

 significant water-holding power in this sand until the moisture 

 content fell to less than 2 per cent. At 1 per cent of soil moisture 

 the seeds took in over 45 per cent of their own dry weight. 



The results of a series of tests running from air-dry (o. 14 per 

 cent) to a little beyond the wilting coefficient (1.3 per cent) are 

 shown in table VII. 



Relation of moisture in no. 2/0 quartz sand 



TO MOISTURE INTAKE OF Xantllium SEEDS 



Soil H,0 

 percentage of absolute 

 weight 



o. 14 (air-dry) . 



OI 59 



°-i75 



0.203 



°-44 



0.81 



1 03 



1-49 



1-79 



214 



Intake H,0 



in percentage of air-dry 



weight 



— 0.306 

 + I.407 

 5.02 

 2I.8l 

 33-98 

 42.40 

 45 64 

 47.46 

 52.06 

 72-85* 



*Four seeds showing incipient germination, hypocotyls 

 averaging 3 mm. long. 



