CHAPTER VI 



THE ROOT SYSTEMS OF PLANTS 



The great depth and high fertihty 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 sj^stems 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 develojoment, the growth of the plant above 



G 81 



