RAPHANUS SATIVUS 



305 



large, secondary xylem vessels are reticulate or pitted and are 

 surrounded by small thick-walled cells. The secondary phloem is 

 comprised of sieve tubes, companion cells, and parenchyma. 



-par 



Fig. 153. Sector of old stem in transection showing vascular bundle: ca, cambium; ep, 

 epidermis ; mech, mechanical tissue ; par, cortical parenchyma ; pel, pericyclic fibers ; ph 1, 

 primary phloem ; /?^ i, secondary phloem ; />/, pith ; r^, medullary ray ; atj i, primary xylem; 

 xy 1, secondary xylem. 



