So ELEMENTARY BIOLOGY. [CHAP. 



d. Beneath the epidermis several layers of large 

 rounded cells containing chlorophyll (parenchyma 

 of the bark). 



e. The medullary rays : radiating rows of paren- 

 chymatous cells uniting b and d: not quite con- 

 tinuous, being interrupted by the cambium zone 



(/r). 



/. The fibro-vasciilar bundles, lying between the 

 medullary rays ; commencing at the side nearest 

 the pith, note 



a. The large openings formed by the transverse 

 sections of the spiral vessels and ducts. 



p. The small thick-walled wood-cells, wedged in 

 between the vessels. These two (a and /5) 

 form the wood or xylem of the bundle. 



y. The cambium zone: granular-looking, and 

 composed of small angular thin- walled cells. 



8. The bast or phloem. It presents internally 

 thin-walled cells of various sizes, the bast 

 parenchyma and bast vessels or sieve tubes. 

 Externally it appears in cross section to be 

 composed of rounded cells with thickened 

 walls ; the bast fibres or liber. Draw the section. 



3. Cut a transverse section through a node, and com- 

 pare it with that through the internode. 



4. Cut a thin longitudinal section through part of an 

 internode (if necessary the bit of stem may be im- 

 bedded in paraffin first), and mount it in water; 



