ABSOEPTION FROM THE SOIL BY PLANTS 237 



soil water from a well and concentrated plant sap as the two 

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

 the soil water were to 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 the stem and leaves. 



253. Root surface. Since water 

 is absorbed only through the 

 surfa.ce of roots, it follows 

 that the rate at " which 

 water will be taken up 

 will be affected by the 

 amount of absorbing sur- 

 face possessed by the roots. 

 The amount of surface on 

 each rootlet is very small, 

 for only the part within a 



very few inches of the FIG. 118. Root hairs 



tip is permeable to water. 

 The older and larger parts 

 of the root are covered by 

 a bark, or cork-like layer, which is almost waterproof. Exten- 

 sive branching of the roots and the presence of root hairs 

 increase the surface of root exposure. 



The root hairs are hair-like projections (fig. 117) 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 quarter of an inch 

 from the tip and extends back as much as an inch or more. 



These hairs add very much to the absorbing 



surface, and they assist in anchoring the 



root in the soil. Highly magnified 



