HYGROSCOPIC WATER IN THE SOIL 103 
sible to rid any natural substance wholly of water 
without heating it to a high temperature. This 
water which, apparently, belongs to all natural 
objects is commonly called hygroscopic water. 
Hilgard states that the soils of the arid regions con- 
tain, under a temperature of 15° C. and an atmos- 
phere saturated with water, approximately 54 per 
cent of hygroscopic water. In fact, however, the 
air over the arid region is far from being saturated 
with water and the temperature is even higher than 
15° C., and the hygroscopic moisture actually found 
in the soils of the dry-farm territory is considerably 
smaller than the average above given. Under the 
conditions prevailing in the Great Basin the hygro- 
scopic water of soils varies from .75 per cent to 34 per 
cent; the average amount is not far from 14 per cent. 
Whether or not the hygroscopic water of soils is 
of value in plant growth is a disputed question. 
Hilgard believes that the hygroscopic moisture can 
be of considerable help in carrying plants through 
rainless summers, and further, that its presence pre- 
vents the heating of the soil particles to a point 
dangerous to plant roots. Other authorities main- 
tain earnestly that the hygroscopic soil-water is 
practically useless to plants. Considering the fact 
that wilting occurs long before the hygroscopic water 
contained in the soil is reached, it is very unlikely 
that water so held is of any real benefit to plant 
growth. 
