324 



ELEMENTS OF GENERAL SCIENCE 



we should have been imitating the plant. Of course, if the 

 soil water should be a more concentrated solution than the 

 plant sap, water would be drawn out of the plant and it 

 would die. This is what happens if a strong solution of 

 salt is poured on the grass of the lawn. 



The water which is taken in by the cells of the surface is 



passed from cell to cell 

 farther into the root by 

 osmosis and finally reaches 

 the tubes or pores through 

 which it is carried into 

 1 the stem and leaves. 



326. Root surface. Since 

 water is absorbed only 

 through the surface of 

 roots, it follows that the 

 rate at which it will be 

 taken up will be affected 

 by the amount of absorb- 

 ing surface possessed by 

 the roots. The amount 

 of surface on each rootlet 

 is very small, for only the 

 FIG. 158. Root hairs part within a very few 



These hairs add very mucn to the absorbing inches of the tip is per- 

 surface and assist in anchoring the root in meable to wafcer> The 

 the soil. Highly magnified 



older and larger parts of 



the root are covered by a bark, or corklike layer, which is 

 almost waterproof. Extensive branching of the roots and the 

 presence of root hairs increase the surface of root exposure. 

 The root hairs are hairlike projections (fig. 157) which 

 grow out from the surface of the youngest rootlets to a 

 length of an eighth of an inch in some cases, clothing the 

 end of the root in a " fuzz." They are not found at the tips 

 of the roots, but the zone covered by them begins about a 



