ROOTS 



49 



mainly through the root-hairs. These are delicate, hair- 

 like outgrowths from the epidermis of the root. They 

 are, as seen in Fig. 11, thin-walled tubes, of nearly uniform 

 diameter, closed at the outer end and opening at the inner 

 end into the epidermis-cell from which they 

 spring. The relation of each hair to the 

 epidermis-cell is still better shown in Fig. 

 23, which represents a very young root- 

 hair and a considerably older one. 



61. Absorption of Water by Roots. - 

 Many experiments on the 

 cultivation of corn, wheat, 

 oats, beans, peas, and other 

 familiar plants in water have 

 proved that some plants, at 

 any rate, can thrive very 

 well on ordinary lake, river, 

 or well water, together with 

 the food which they absorb 

 from the air (Chapter XII). 

 Just how much water some 

 kinds of plants give off (and 

 therefore absorb) per day 

 will be discussed when the 

 uses of the leaf are studied. 

 For the present it is suffi- 

 cient to state that even an 

 annual plant during its lifetime absorbs through the roots 

 very many times its own weight of water. Grasses have been 

 known to take in their weight of water in every twenty- 

 four hours of warm, dry weather. This absorption takes 



A B 



FIG. 23. 



A, a very youug root-hair ; B, a much 

 older one (both greatly magnified). 

 e, cells of the epidermis of the root ; 

 n, nucleus ; s, watery cell-sap ; p, 

 thicker protoplasm, lining the cell- 

 wall. 



