THE PLANT AS AFFECTED BY WATER 135 



wanting when the water supply during growth has been 

 insufficient. 



Insufficient water during growth injures the quality of 

 tobacco. Leaves thus affected have a peculiar spotted 

 appearance when cured, and do not " sweat " properly. 



231. Cultivation of the soil. Crumbling of the surface 

 soil 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 by capillary attraction to 

 the surface where evaporation chiefly occurs. An air-dry 

 surface layer of crumbled soil also tends to prevent 

 evaporation by keeping the soil cooler beneath. 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 evapora- 

 tion. Some gardeners cultivate their hoed crops as soon 

 as possible after rains for the main purpose of breaking 

 this crust and thus stopping the capillary action. 



Cultivation is also beneficial by aerating the soil (93). 

 The roots of plants should never be forgotten nor ig- 

 nored in cultivating crops (109). 



232. Mulching tends to prevent drought, by interposing 

 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, manure, shavings, sawdust, spent tan and sand 

 are all useful for mulching, but the first four named are 

 generally preferable to the others, especially if free from 

 weed seeds. 



Growing plants tend to dry the soil because the root- 

 hairs continually draw in soil water and force it into the 



