70 



PLANT LIFE. 



In both cases, the differentiation of cells produced at the 

 growing jioint resulis in the formation of three characteristic 

 parts (.)f the root, namely, (i) an outer layer or layers, the 

 epidermis : (2) an inner region, the stele ; (3) between these, 

 the cortex. 



78. I. The epidermis usually becomes man \' -layered. 

 At the apex it constitutes the rout-cap (ep, fig. 83). On the 

 other parts of the root it sometimes sloughs 

 off enlireU', exposing the cells of the cortex 

 itself, as in the monocotyledons (lilies, 

 grasses, sedges, etc.); or, more commonly, 

 only the outer layer sloughs off, leaving the 

 innermost as the covering of tlie cortex. 



79. [a) Eoot-hairs. — Those cells which 

 form the surface of the root, 

 whether they be the original 

 epidermis or cortical ones 

 which have been exposed 

 by its loss, Usually de\elojj 

 a large number of hairs, 

 known as ruot-Iiairs ( fig. 

 84). These root-hairs are 

 branches of the superficial 

 cells (fig. 85), and may be 

 looked upon as sim])le ex- 

 tensions of them, as the 

 finger of a glove is the 

 extension of its palm. Only 

 one root-hair arises from a 

 superficial cell. Tlicy are 

 usually unbranched and -without trans\-ersc partitions. Only 

 in rare cases are they wanting. They lixe for a shorter 

 or longer time, but are always, as compared with the 

 duration ol the root, (juite transient. The older part of the 



Fig. 85. — I'wo ruot-hairs showing structure 

 and relation to superficial cells of root ; 

 grown in water and therefore not distorted 

 as in fig. 84. --J. the younger; />, older, 

 nearly mature. «, nucleus embedded in 

 cytoplasm; vaciu;ile single and very large. 

 Highly magnified. — .After Frank. 



