154 



He describes soils in California which can mature crops with- 

 out any rain during the growing season, and without irriga- 

 tion. 



All the water held in the soil by capillary action is not 

 available for plants, but the percentage which can be absorbed 

 is greater in coarse-grained soils, like sand, than in those of 

 finer texture. Experiments by Sachs showed that in a clay 

 with a water capacity of 52.1 percent, only 44.1 percent could 

 be used by a tobacco plant, leaving 8 percent of unavailable 

 water; while in a sand with 20.8 percent water capacity, 19.3 

 percent, very nearly the whole amount present, was available. 

 These results are substantiated in the held, plants suffering 

 from drought in some soils with 15 percent water, while in 

 others, of more sandy nature, they are still healthy with a 

 water content of less than 5 percent. 



In contrast with the foregoing data mention should be 

 made of the experiments of Livingston and Jensen ('04), who 

 have shown that the fertility of the soil is dependent on the 

 size of the component particles, and that coarseness alone "can 

 produce sterility in spite of a plentiful supply of water." It is 

 entirely possible, then, that the mere size of the sand particles 

 may bean important ecological factor in the sand region along 

 the Illinois River. 



But independently of the quantity of water present in the 

 sand, the precipitation must have a marked bearing on the 

 quantity and kind of available plant food. In all the sand re- 

 gion, as before stated, there is no surface drainage. Water 

 falling as rain sinks at once into the sand, and the excess is re- 

 moved by underground drainage to the Illinois River, where it 

 issues through countless springs along the east bank. After 

 the heaviest rains, water may collect for a time in the blow- 

 outs and interdunal depressions, but it soon sinks into the sand. 

 By this rapid percolation through the upper layers of sand 

 much of the soluble matter must be dissolved and carried down 

 to the level of the ground-water, which in this region is never 

 less than twenty feet below the surface ( Leverett. '96, p. 759; 



