PLANT GROWTH IN DRY AREAS 113 



dependent on the favorable conditions for growth viewed 

 from the .standpoint: (1) of the sufficiency of the water 

 supply; (2) of the abundance of the plant food, and (3) of 

 the favorable character of the mechanical soil conditions 

 that favor root penetration. Such activity in root growth 

 is specially important in the early stages of growth. 



Relatively deep rooting is specially important in 

 plants in dry areas. Such rooting enables them to secure 

 increased moisture and also increased plant food. The 

 moisture supply near the surface is usually greater in 

 humid than in dry areas, hence the greater tendency in 

 root growth in the latter to go down much more deeply 

 than in the former. Corn roots in these have been known 

 to ramify the soil in all directions to the depth of 7 or 8 

 feet, and the roots of small cereals have been traced in 

 the subsoil to the depth of 10 feet. These are of course 

 extreme instances. They also find more easily digestible 

 plant food than is usually found in the subsoils of 

 humid areas. The generally favorable physical character 

 of the subsoils of western areas for root penetration after 

 they have been moistened by water favors deep growth 

 in the roots, and this brings to the plants greater immuni- 

 ty from the hazard that would otherwise come to them 

 in time of drought. Where plants are irrigated they estab- 

 lish a root system near the surface, as there they may 

 find ample water to supply their needs. 



Strong root growth is also important, owing to the 

 closeness of the relation that obtains between develop- 

 ment in the roots and growth above ground. Especially 

 is this relation important with reference to the production 

 of seed. It has been claimed, and it would seem properly 

 so, that there is some relation between strong root devel- 

 opment and the abundant stooling that comes to the 

 small cereals in dry areas. No measures, therefore, 

 should be overlooked, when preparing the soil for seed, 



