WHERE FOOD COMES FROM 



117 



to prevent the complete removal of the sand by the winds. The 

 hillocks formed by clumps of such plants may continue to en- 

 large for years, and to give protection to other kinds of plants 

 until the earth has become compact (Fig. 68). 



Roots do not generally put forth buds or shoots, but the roots 

 of a few plants do so— certain willows, poplars, and hawthorns. 





X.:^L-.aQt!^ 



Fig. 68. Sand dunes at Pine, Indiana 



The roots and underground stems of the grass Calamovilfa longijolia bind together 



the grains of sand, and larger and larger soil masses are gradually formed. Barren 



sand is blown about by the winds. (From photograph by Dr. George D. Fuller) 



Roots of such plants can therefore be used for propagating the 

 species. In some plants the roots will form new shoots if the old 

 shoot is completely removed or destroyed. Roots frequently 

 arise from stems or leaves, thus making possible the propaga- 

 tion of plants by means of cuttings (see Fig. 69). Blackberry 

 and raspberry bushes are frequently propagated by layering, 

 which consists of bending the flexible stems outward and bury- 

 ing the tips in the ground. New roots are formed on the covered 

 portions, and, later, buds form new shoots. The old connecting 



