202 



BOTANY AND PHARMACOGNOSY, 



the medullary rays outside of the cambium, and the tissue formed 

 by the phellogen. 



-M 



Fig. 112. Fully developed secondary structure in root. Transverse section of root 

 of pea (Pisum) at the end of the summer's growth: E, some epidermal cells with fragments 

 of root hairs; C, primary cortex; EN, endodermis; K, cork; B, bast fibers; SC, secondary 

 cortex; S, leptome; T, hadrome; W, wood fibers; WP, wood parenchyma; M, medullary 

 rays; the hadrome (or vessels) and leptome (or sieve) forming open collateral fibrovascular 

 bundles, these being found in dicotyledons with but few exceptions. 



The following diagram of the secondary structure of a dicoty- 

 ledonous root may be of assistance in understanding the origin 

 and relation of the tissues comprising it : 



