18 



THE ECOLOGY OF ROOTS 



the soil. In sandy regions and especially in regions of shifting sand 

 dunes, such as occur along sea coasts, there are certain plants, par- 

 ticularly some kinds of grasses, that are known as "sand binders" 

 because of their ability to grow in the unstable sand and often to 

 check its movements or even to stop it entirely (Fig. 5). The move- 

 ment of the sand in such a place is of course due to wind action, 

 and the sand binding plants are often planted along railroads and 

 the borders of farms to prevent the encroachment of the sand 

 through the agency of wind. 



Fig. b.—Hudsonia tomentosa. A sand binding plant. (Photograph by 



A. G. Eldredge.) 



7. Food Accumulation.— ]Many plants have thick fleshy roots 

 which serve the somewhat special function of store houses for accu- 

 mulated foods. This is especially true of plants with tap roots 

 such as beets, parsnips and dandelions. It is also true of many 

 plants with fascicled or tuberous roots, as the dahlia and the sweet 

 potato. 



Most of these storage roots accumulate starch and in some, the 

 sweet potato for example, there is not much except starch. Some, 

 however, like the beet, accumulate sugar in addition to starch, and 

 the dandelion and the dahlia as well as many other members of 

 the composite family accumulate considerable quantities of inulin, 

 a soluble carbohydrate. Practically all of these thickened roots 

 also accumulate water and in many cases this is more important 

 than the accumulation of food. Many desert plants have immense 



