8 
SOILS AND ALKALI. 
the ordinary water capacity is much less than the sat¬ 
urated capacity : 
Heavy 
Quartz. Clay. Saw-dust. Spar. 
Saturated, . . per cent., 49 46 76.4 39.2 
Water capacity, “ “ 13.7 24.5 45.6 11.7 
During dry weather plants require a soil which is re¬ 
tentive and absorptive of atmospheric moisture. The 
amount of this retention is generally in direct ratio to two 
factors, viz., the amount of organic matter and its state 
of division. The capillary water of the soil is very closely 
related to its percolating power, since all waters in the soil 
are governed in their movements what is known as 
capillary force. Liebenberg has shown that this move¬ 
ment may be either upwards or downwards, according as 
the atmosphere is dry or supplies soil-saturating rain. 
The water absorbed by the roots passes into the plant cir¬ 
culation, and the greater part is evaporated from the 
leaves. Where the supply of water is insufficient, the 
plant wilts, and if the evaporation long continues in ex¬ 
cess of the supply obtained from the soil, the plant must 
die. The experiments of Hellriegel have shown that any 
soil can supply plants with all the water they need, and 
as fast as they need it, so long as the moisture within the 
soil is not reduced below one-third of the whole amount 
that it can hold. The quantity of water required and 
evaporated by different agricultural plants during the 
period of growth has been found to be as follows: 
One acre of wheat exhales 409,832 lbs of water. 
“ “ “ clover “ 1,096,234 “ “ “ 
“ “ “ sunflowers “ 12,585,994 “ “ “ 
“ “ “ cabbage “ 5,049,194 “ “ “ 
“ “ grape-vines “ 730,733 “ “ “ 
“ “ “ hops “ 4,445,021 “ “ “ 
Dietrich estimates the amount of water exhaled by the 
foliage of plants to be from 250 to 400 times the weight 
of dry organic matter formed during the same time. 
