CHAPTER VI 
THE ROOT SYSTEMS OF PLANTS 
Tue great depth and high fertility of the soils of 
arid and semiarid regions have made possible the 
profitable production of agricultural plants under a 
rainfall very much lower than that of humid regions. 
To make the principles of this system fully under- 
stood, it is necessary to review briefly our knowl- 
edge of the root systems of plants growing under 
arid conditions. 
Functions of roots 
The roots serve at least three distinct uses or 
purposes: First, they give the plant a foothold in 
the earth; secondly, they enable the plant to secure 
from the soil the large amount of water needed in 
plant growth, and, thirdly, they enable the plant 
to secure the indispensable mineral foods which can 
be obtained only from the soil. So important is 
the proper supply of water and food in the growth 
of a plant that, in a given soil, the crop yield is usu- 
ally in direct proportion to the development of the 
root system. Whenever the roots are hindered in 
their development, the growth of the plant above 
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