24 



ROOTS 



31. General structure of roots. The general structure of the 

 very young root can be partially made out by examining the 

 entire root with a moderate magnifying power. Often the whole 

 is sufficiently translucent to allow the interior as well as the 



exterior portion to "be 

 studied while the root 

 is still alive and grow- 

 ing. 



The main bulk of 

 the root is composed of 

 a central cylinder and 

 the cortical portion 

 which surrounds it. 

 The outermost part of 

 the cortex is a layer of 

 cells forming a thin 

 skin known as the epi- 

 dermis. The tip of the 

 root is covered by a 

 mass of loosely attached 

 cells forming the pro- 

 tective root cap. 



On examining Figs. 

 20 and 21, the cylin- 

 ders of which the root 



W, root cap; i, younger part of cap; z, dead cells is made up are easily 



separating from cap; s, growing point; o, epi- _.. ,. > -\ j ,i 



dermis;p', intermediate layer between epidermis QlStingUlsnea, a 



and central cylinder ; p, central cylinder, in which main constituent parts 

 the fibro-vascular bundles arise. After Wiesner 



of each can be made 



out without much trouble. The epidermal cells are seen to be 

 somewhat brick- shaped, many of them provided with extensions 

 into root hairs. Inside the epidermis lie several layers of rather 

 globular, thin-walled cells, and inside these a boundary layer 

 between the cortical or bark portion of the root and the central 

 cylinder. This latter region is especially marked by the presence 



FIG. 20. Lengthwise section (somewhat dia- 

 grammatic) through root tip of Indian corn, 

 x about 130 



