THE STRUCTURE OF THE ROOT 



39 



The newly formed cells become converted into wood, 

 so that a strand of wood, called secondary wood, is 

 formed inside each bast bundle. The cambium layer 



FIG. 1 6. Thickening of root ; px, primary wood ; .SAT, secondary 

 wood; c, cambium; en, endodermis. X8o. (After Kny.) 



extends laterally round the bast bundle, so that it tends 

 to pass up towards the outer edge of the wood bundle on 

 each side. By the time a little mass of wood has thus 

 been formed between each bast strand and the centre 

 of the root, the cells of the pericycle outside the 

 wood bundles divide by similar tangential walls, so 



