CHAPTER III 



ROOTS 



24. Structure of roots. A very young root is often translu- 

 cent enough to be examined directly with a low power of the 

 compound microscope. It is then seen to be composed of an 



exterior hollow cortex, nearly 

 cylindrical in form, and a 

 central cylinder within the 

 cortex. The outermost por- 

 tion of the cortex is a layer 

 of somewhat brick-shaped 

 cells constituting the epider- 

 mis, and from some of the 

 cells of the epidermis root 

 hairs often spring (Fig. 6). 

 The growing tip of the root 

 is covered with several layers 

 of cells, most of them dead 

 or dying, constituting the 

 root cap. 



A moderately magnified 

 cross section of a very young 

 dicotyledonous root shows 



c, epidermis; c, cellular layer of cortex; the epidermis as a narrow 



cyl, central cylinder ; w, woody strands of ring, Surrounding a much 



fibrovascular bundles of central cylinder. j / fi j 



Alternating with these are much smaller broader ring O the Unde 



strands of bast fibers, not shown in the dia- lying COrtex, and within this 



gram. Modified after Bonnier and Sablon _f , , . , . 



the central cylinder, contain- 

 ing a fixed number of radially arranged fibrovascular bundles. 

 The relative proportions of the several regions can be under- 

 stood from Fig. 18. 



24 



. 

 : ~~ ^ 



FIG. 18. Diagrammatic cross section of 

 a very young dicotyledonous root 



