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 

 i g 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 

 the epidermis as a narrow 

 ring, surrounding a much 

 broader ring of the under- 

 lying cortex, and within this 

 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 



e, epidermis; c, cellular layer of cortex; 

 cyl, central cylinder ; w, woody strands of 

 fibrovascular bundles of central cylinder. 

 Alternating with these are much smaller 

 strands of bast fibers, not shown in the dia- 

 gram. Modified after Bonnier and Sablon 



