152 



Of far greater importance as an ecological factor is the sand 

 in its relation to the water supply and, indirectly, to the sup- 

 ply of plant food. It is a known fact that coarse soils, such as 

 sands, have a smaller capacity for water than fine soils, the 

 water being held as a thin film surrounding the soil par- 

 ticles, and surface-tension being less effective over large sur- 

 faces than over small ones. The water capacity of soils, accord- 

 ing to experiments by Sctiuebler and Wollny (Warming, '96, 

 p. 51), is least in quartz sand. Schimper ('98, p. 94) states that 

 the water which loose sand can hold is but 13.7 percent of its 

 own volume, while clay has a capacity of 40.9 percent. Exper- 

 iments by the United States Bureau of soils (Whitney and 

 Hosmer, '97, pp. 14-17) on sandy soil in Alabama showed a 

 water content varying from maxima of 11 percent and 14 per- 

 cent after rains to minima as low as 1 percent and .6 percent 

 during periods of drought. This is in marked contrast with 

 the results of similar experiments on prairie sod in Kansas, 

 where the water content varied from a maximum of 15 percent 

 to a minimum of 7.4 percent, and on blue-grass land in Ken- 

 tucky, where the average content was over 20 percent, and 

 the line of drought, at which the vegetation began to suffer, 

 was at 15 percent. The actual size of the particles composing 

 these soils is not stated. Warming (/. c.) quotes Wollny as 

 saying that the water capacity of quartz sand composed of 

 particles 1-2 mm. in diameter is only one tenth that of sand 

 with particles .01-07 mm. in diameter. No data are as yet avail- 

 able concerning the actual water capacity of the Miami fine 

 sand in Illinois, but it must be much lower than that of the 

 other soil types of the district. 



The power of capillary action to lift water from lower 

 levels is also less in coarse-grained than in fine-grained soils; 

 and in fine sand, according to Ramann (Warming, '96, p. 50), 

 water will rise only 40 centimeters, or about 16 inches, above 

 the surface of the ground-water. In sand with grains from .25 

 mm. to . I mm. in diameter, such as constitutes 62 percent of 

 the Miami fine sand in Mason county, water should rise by 

 capillary attraction from 19 to 48 inches. It is evident that no 



