330 Introduction to Botany. 



and that the water thus caught may be retained by the 

 mulch of loose soil at the surface. The success of tree 

 claims in the semi-arid regions of the United States de- 

 pended largely upon the degree of persistence in this 

 mode of treatment. Figure 177 is a drawing from a pho- 

 tograph of a claim which was planted with trees and neg- 

 lected, while Figure 178 shows the result of cultivation in 

 the neighborhood of the neglected claim. 



In regions where the rains occur frequently during the 

 growing season, though not in sufficient amount to produce 



FIG. 178. 



Drawing from a photograph of a tree claim in western Kansas that has been 

 properly cultivated. 



a perennial water supply in the deeper strata of the soil, 

 grasses predominate, while trees, with the exception of those 

 of xerophilous character, such as occur in savannas, are 

 absent. The dry atmosphere and strong winds which are 

 apt to occur in treeless regions are much less inimical to 

 grasses than to trees, because the former keep close to the 

 ground, where the adverse conditions are less pronounced. 

 The character of the soil may also impress its stamp upon 

 the flora of a region. Thus, to take examples from a single 

 genus, CEnothera laciniata occurs in dry sandy soils, (Eno- 

 thera rhombipetala is a prairie plant, and CEnothera Mis- 



