ROOT SYSTEM 



269 



nucleus- 



epidermal 

 celiacs 



Figure 261. — Root Hairs. 



called the xylem. These cells carry water from the root 

 upwards. The outer part of the bundle (the phlo&m) 

 is of a softer tissue and contains the sieve vessels which 

 carry liquid food downward. 



The epidermis of the rootlets is covered with rout 

 hairs, which are really much elongated cells (Figure 261). 

 While root hairs help to 

 hold a plant firmly in 

 place, their main use is 

 to take up water from 

 the soil. The cell walls 

 are thin and are lined 

 with a thin layer of pro- 

 toplasm. Water is taken 

 in through the walls of the cells by osmosis (page 3). The 

 root hairs which grow in soil apply themselves closely to 

 particles of it, and take from them the thin film of water 

 with which each is covered. On this account the hairs or 



rootlets grown in soil are much more 

 irregular in shape than those grown in 

 water or in moist air. Unless a plant is 

 removed carefully, all the root hairs are 

 broken off and remain in the ground. 



Another statement is frequently 

 made in discussing the uses of rout 

 hairs, namely, that by means of an 

 acid which they secrete, they dissolve 

 minerals in the soil so that they can 

 be taken up by water and carried into 

 the plant. This is based on the fact that a seedling 

 grown on a polished marble plate will corrode the sur- 

 face, and on other experiments. Researches recently 

 made prove conclusively that root hairs do nut secrete 

 acid. 



Figure 262. 

 Cap. 



Root 



