HINTS ON SOILS AND FERTILIZERS 31 
Of course, good tilth is to be desired in a fertile 
soil, but a soil rich in fertility, or plant food, 
may seriously lack good tilth. By the same 
token, a soil possessing good tilth may be 
quite lacking in soil fertility. For instance, a 
sandy soil usually has good tilth, or we may 
say that it is easily worked up. But the chances 
are that this sandy soil is not very rich in 
soil fertility. Hence, we see that there is no 
direct correlation between the two factors. 
FUNCTIONS OF SOIL WATER 
There are several very important reasons why 
plants require water. We have already seen 
something about the activity of water as a car¬ 
rier of plant food from the roots of the plant 
to the leaves, and also noted the fact that the 
water carries the manufactured plant food to 
the various parts of the plant from the leaves. 
The water performs other important functions 
in the plant as well. It is one of the forms 
of food that the plant uses in the process of 
growing. 'The constant evaporation that goes 
on from the leaf surface of the plant has a 
cooling effect upon the plant, thereby prevent¬ 
ing it from succumbing to the intense heat of 
the hot summer temperature. The presence of 
water also prevents the plant from wilting. 
We have noted in a previous chapter that 
crops are ordinarily very large consumers of 
water during the growing season. In one case, 
we noted that it took over one hundred and 
fifty barrels of water to make possible the pro- 
