76 STKUCTUKAL BOTANY 



really the innermost layer of the cortex. The rest of 

 the cortical tissue consists of living parenchymatous 

 cells, with thin cellulose walls. They do not, of 

 course, contain any chlorophyll, because the roots in 

 the earth receive no light, without which chlorophyll 

 cannot be formed, though the plastids may be present. 



The outermost layer of the young root, corresponding 

 in position to the epidermis of the stem, consists of 

 thin-walled living cells, many of which grow out into 

 long hairs (see Fig. 28). These root-hairs are very 

 important organs; they take up all the food which 

 the plant obtains from the soil. Each root-hair is a 

 single cell, with protoplasm and a nucleus, and a thin 

 cell-wall. The delicacy of the outer cell-walls, and 

 the absence or slight development of cuticle, are points 

 in which the external layer of the root differs from 

 the epidermis of the shoot. The meaning of these 

 differences is, that the epidermis of the stem is a 

 protective layer, which among other duties has to 

 hinder the passage of water out of the plant, while 

 the external tissue of the root is absorptive (so long, 

 that is, as the root is quite young), and has to admit 

 into the plant water and various food-substances which 

 are dissolved in it. Partly because of this great 

 difference in function, and partly on account of some 

 differences in the development, it is better not to 

 speak of the external layer of roots as an epidermis, 

 but to call it the piliferous layer, i.e. the layer which 

 produces the root-hairs. 



These root-hairs grow between the small particles 

 of soil, and attach their ends to them quite firmly, so 



