88 



BOTANY 



Young embryo of corn, 

 showing root hairs 

 (R.H.) and growing 

 stem (-P.)' 



Fibrovascular Bundles. — Collections of such tubes and sup- 

 porting woody cells together make up what is known as fibro- 

 vascular bundles. 



Structure of a Root Hair. — The cells of 

 the cortex are almost uniform in character. 

 The outmost layer, however, differs from 

 the rest of the cortex. This layer is 

 called the epidermis. It is the prolongations 

 of the cells of the epidermis that form the 

 structures we have already seen and know 

 as root hairs. 



Let us now take out one of the small 

 radish seedlings from the pocket garden, 

 mount it in water, and examine it under 

 the low power of the microscope. A single 

 root hair will be found to be a long round 

 structure, almost colorless in appearance. 

 The wall, which is very flexible and thin, is 



made up of cellulose, a substance somewhat like wood in chemical 



composition, through which fluids may easily pass. If we had a 



very high power of the microscope focused upon this cellulose 



wall, we should be able to find under it another 



structure, far more delicate than the cell wall. 



This is called the cell membrane. Clinging 



close to the cell membrane is the protoplasm 



of the cell, which in the root hair is found 



close to the membrane. The interior of the 



root hair is more or less filled with a fluid 



called cell sap. Forming a part of the living 



protoplasm of the root hair, sometimes in the 



hairlike prolongation and sometimes in that 



part of the cell which forms the epidermis, is 



found a nucleus. The protoplasm, nucleus, 



and cell membrane are alive; all the rest of 



the root hair is dead material, formed by the 



activity of the living substance of the cell. 



The root hair is a living plant cell with a wall 



Diagram of a root 

 hair: CM., cell 

 membrane; C.S., 

 cell sap; C.W., cell 

 wall; P, proto- 

 plasm; N, nucleus; 

 S, soil particles. 



