MORPHOLOGY OF HIGHER PLANTS. 315 



Some differences are, however, quite noticeable in some instances, 

 as in the thick roots of Beta, Radish, etc., where the wood paren- 



M 



FIG. 175. Fully developed secondary structure in root. Transverse section of root 

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

 of root-hairs; C, primary cortex; EN, endodermis; K, pericambial cork; B, bast fibers; 

 SC, secondary cortex; S, sieve; T, tracheae; W, wood fibers; WP, wood parenchyma; 

 M, medullary rays; the tracheae (or vessels) and leptome (or sieve) forming open collateral 

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



chyma is usually abundant, thin-walled, and not lignified, the 

 annual rings also being mostly indistinct. 



The characteristic distinguishing the primary and secondary 



