REGULATING THE EVAPORATION 1638 
summer cultivation is somewhat more difficult, but 
must be practiced for the greatest certainty of crop 
yields. Potatoes, corn, and similar crops may be 
cultivated with comparative ease, by the use of 
ordinary cultivators. With wheat and the other 
small grains, generally, the damage done to the crop 
by harrowing late in the season is too great, and 
reliance is therefore placed on the shading power of 
the plants to prevent undue evaporation. However, 
until the wheat and other grains are ten to twelve 
inches high, it is perfectly safe to harrow them. The 
teeth should be set backward to diminish the tearing 
up of the plants, and the implement weighted enough 
to break the soil crust thoroughly. This practice 
has been fully tried out over the larger part of the 
dry-farm territory and found satisfactory. 
So vitally important is a permanent soil mulch for 
the conservation for plant use of the water stored in 
the soil that many attempts have been made to de- 
vise means for the effective cultivation of land on 
which small grains and grasses are growing. In 
many places plants have been grown in rows so far 
apart that a man with a hoe could pass between 
them. Scofield has described this method as prac- 
ticed successfully in Tunis. Campbell and others 
in America have proposed that a drill hole be closed 
every three feet to form a path wide enough for a 
horse to travel in and to pull a large spring tooth 
cultivator, with teeth so spaced as to strike between 
