90 AGRICULTURE 



for woodland. The roots bind the soil together and prevent 

 washing. 



As a rule, shallow plowed land washes most, unplowed land 

 less, and deep plowed land least of all. 



EXERCISE 



1. Take two thrifty plants of the same kind and as near the same size 

 as you can get. Set one in a glass jar filled with moist, mellow soil ; 

 set the other in a flowerpot of similar soil, with a layer of gravel at the 

 bottom. Water equally and observe the results on growth. In three or 

 four weeks soak the soil away, and examine the root development of 

 each plant. 



2. Grow timothy and alfalfa in flowerpots. Set these pots in pails 

 of water deep enough to cover their tops. Which plant suffers more 

 from lack of drainage? 



IRRIGATION 



Arid and Semi-arid Region. A soil may contain abundant plant 

 food but be unproductive because moisture is lacking. This is 

 the case in the arid and semi-arid region of the United States, 

 which lies between the ninety-fifth meridian and the Rocky Moun- 

 tains, and extends from Canada almost to the Gulf of Mexico. It 

 includes all or part of the states of Arizona, California, Colorado, 

 Idaho, Kansas, Montana, Nebraska, Nevada, New Mexico, North 

 Dakota, Oklahoma, Oregon, South Dakota, Utah, Texas, Washing- 

 ton, and Wyoming, a vast region of three hundred million acres 

 of land. The ocean breezes are deprived of moisture by the moun- 

 tains and plains to the east and west, and come dry and parched to 

 this Great Basin. 



Uneven Rainfall. Where the rainfall is abundant or excessive, 

 it may be so uneven as to allow the crops to suffer for moisture. 

 In parts of Florida where the yearly rainfall is sixty or seventy 



