Plants as Affected by Insufficient Water. 133 
Insufficient water during growth injures the quality of 
tobacco. Leaves thus affected have a peculiar spotted ap- 
pearance when cured, and do not ‘sweat’ properly. 
232. Crumbling of the Surface Soil (cultivation) 
tends to Prevent Drought, since it greatly lessens the 
points of contact in the soil particles, and thus interferes 
with the rise of the soil water to the surface through capil- 
lary attraction. An air-dry surface layer of crumbled soil 
also tends to prevent evaporation by keeping the soil be- 
neath cooler. Since evaporation of the soil water occurs 
almost exclusively at the surface of the ground, cultivation 
aids materially in conserving moisture for the use of plants. 
A puddled crust on the surface of the soil, as is formed 
by rain on soils containing clay, tends, on the other hand, 
to restore capillary action, and thus to promote evaporation. 
Some very thorough gardeners cultivate all their hoed crops 
as soon as possible after rains for the main purpose of break- 
ing this crust, and thus stopping the capillary action. 
Cultivation is also beneficial by aerating the soil (91). 
The roots of plants should never be forgotten nor ignored 
in cultivating crops. 
233. Mulching tends to Prevent Drought by inter- 
posing a layer of poor-conducting material between the 
ground and the sun’s rays. This keeps the surface soil 
cooler and so checks evaporation. 
The best mulching material is the one that conducts both 
heat and moisture slowest. Straw, marsh hay, leaves, ma- 
nure, shavings, sawdust, spent tan and sand are all useful 
for mulching, but the first four named are generally prefer- 
able to the others, especially if free from weed seeds. 
234. Irrigation, i. e., the extensive watering of out- 
door plants, is the final remedy for drought. It is a neces- 
