22 



HORTICULTURE FOR SCHOOLS 



FIG. 9. Root/- 

 hairs on young 

 radish. 



39. Functions of roots. Plants depend on the roots for 

 the absorption from the soil of water and substances in solu- 

 tion to be manufactured by 

 certain cells into food material. 

 The main part of 

 the root does not 

 absorb such ma- 

 terial, but the 

 absorption is by 

 specialized cells 

 known as root- 

 hairs (Fig. 9). A 

 root-hair is a 

 single, elongated, 



***** Cs f> -m^mm^/ living cell, consist- 



ing of the usual 

 parts of the cell 

 (Fig. 10). Root-hairs are pro- 

 duced by the outside (epider- 

 mal) tissue of the root, and occur near the growing point of the 

 root. If plants are dug up carefully and the soil washed from 

 the small fibrous roots, the root-hairs can be seen readily. The 

 root-hairs are short-lived and are found only on the young roots 

 near the tips. As the roots get older, the root-hairs farthest 

 back gradually die and are replaced by those growing near 

 the tip. 



The root-hairs absorb solutions from the soil by osmosis. 

 The process of osmosis can easily be illustrated artificially by 

 an old experiment. A thistle-tube is filled with molasses or 

 sugar solution, and a membrane such as a pig's bladder or 

 parchment paper is tied across the large end. The tube is 

 then inserted in a beaker of water with the large end down so 

 that the membrane is submerged in water. A rise of liquid 

 in the tube shows that the dilute solution is passing through 

 the membrane into the denser sugar or molasses solution. 



FIG. 8. Tip of root showing root-cap. 



