88 



ROOTS AND THEIR WORK 



Cross section of a young taproot : 

 u, u, root hairs; b, epidermis; c, 

 cortex ; d, fibrovascular cylinder or 

 wood. 



Root Hairs. — Careful examination of the root of one of the seed- 

 lings of mustard, radish, or barley grown in the pocket germinator 



shows a covering of tiny fuzzy 

 structures. These structures are 

 very minute, at most 3 to 4 mm. 

 in length. They vary in length 

 according to their position on the 

 root, the most and the longest root 

 hairs being found near at the point 

 marked R. H. in the Figure. These 

 structures are outgrowths of the 

 outer layer of the root (the epi- 

 dermis), and are of very great im- 

 portance to the living plant. 



Structure of a Root Hair. — A 

 single root hair examined under a 

 compound microscope 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 com- 

 position, 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. 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 some- 

 times 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 



Young embryo of corn, show- 

 ing root hairs (R. H). and 

 growing stem (P.). 



