PLANT STRUCTURE 137 



With this division, the individual increases in size, 

 and this increase is termed growth. The vigor and health- 

 fulness of a plant body is, therefore, dependent on the 

 proper action of each individual cell. Because of this 

 fact, it is necessary that the successful plant grower have 

 an intimate knowledge of the function of each cell and the 

 conditions which favor its healthy action. 

 107. Function of various cells. 



(a) Root-hairs. Root-hairs serve to take the soil 

 water and the food substances which are dis- 

 solved in it, into the protoplasm of the epidermal 

 cells of the root. This is done by the process of 

 osmosis, previously described. All plant foods 

 from the soil must, therefore, be in solution. As 

 root-hairs are located but a short distance from 

 the root-tip, plants feed from the soil only from 

 this part of the roots. No matter how long a 

 root may be, the feeding area is limited to the 

 immediate surface just back of the root-tip. 

 (6) The root-cap. The root-cap cells vary much in 

 size. The inner cells, which are near what is 

 known as the central cylinder, are small, but they 

 gradually increase in size until those on the out- 

 side are quite large. The expansion of cell 

 contents by growth pushes the root through the 

 soil, frequently with sufficient force to cause 

 the roots to penetrate extremely hard substances. 

 The growth of the root in length takes place only 

 at the immediate tip. The outer cells of the root 

 cap, as they increase in size, become function- 

 less and drop off. 



(c) Cells of the vascular bundles. Elongated cells 

 begin near the tip of the root and pass length- 



