EVAPORATION FROM LEAVES 



135 



made by pot experiments. It is impossible to weigh 

 a growing fig tree several times a day, to ascertain 

 its water content, but by placing some such plant as 

 a sunflower in a pot and protecting the soil from 

 evaporation and rainfall, a measured quantity of 

 water can be given it daily and that expired 

 through leaves is thus ascertainable. A single sun- 

 flower stalk with eight leaves was found to lose one 

 pound and fourteen ounces during a warm dry day, 

 one pound and four ounces during another day 

 not so warm, three ounces in a night without dew, 

 while it absorbed four ounces of moisture during a 

 foggy night. It is probable that a common fig bush 

 will transpire no less than a half gallon of water 

 a day during warm growing weather. 



In arid regions, such as Arizona, New Mexico 

 and Nevada, the first step in cultivation is to create 

 an adequate storehouse to hold the scant rainfall 

 in the ground, and by improving the texture of the 

 soil with humus and deep tillage to make the winter 

 precipitation available during the long dry sum- 

 mers when plants draw capillary water toward the 

 surface for their use. 



The following table pictorially represents the im- 

 portance of humus as a means of retaining moisture 

 in the soil: 



Kind of soil 



Sand 



Clay loam . 

 Humus P , . 



Pounds Pounds 

 of moisture, of dry soil. 



19.60 100 

 32.40 100 

 114.60 100 



