46 



ELEMENTARY BIOLOGY 



root than goes out, since, on the one hand, we know that 

 the growth of a hving thing depends upon an excess of income 

 over outgo ; and, on the other hand, we know that the soil 

 water is less concentrated than the juices of the root. The 

 stream of incoming material actually sets up a current of liquid 

 that is forced from the root into the upper parts of the plant. 



^ ^^^.^ 



Fig. 12. Sand dunes at Pine, Indiana 



The roots and underground stems of the grass Calamovilfa Inm^ifolia bind together the 



grains of sand, gradually leading to the formation of larger and larger soil masses. Barren 



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



This can be seen in the flow of sap, as when the sugar maples 

 are tapped for sirup in the spring, and it can also be shown 

 experimentally. 



72. Uses of roots. It is because of the habit of depositing 

 food in their roots that many plants are of especial interest to 

 us. Our common vegetable roots can be shown to contain a 

 great deal of food, such as starch, sugar, and proteins. Although 

 our fleshy vegetables contain from about 8o per cent to 90 per 

 cent of water after the skin is removed, they are still worth 



