8o 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-vascular 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. 



/?. The small thick-walled wood-cells, wedged in 

 between the vessels. These two (a and ft) 

 form the wood or xylem of the bundle. The 

 last or phloem. It presents internally thin- 

 walled cells of various size, the bast paren- 

 chyma and bast vessels or sieve tubes. Ex- 

 ternally it appears in cross section to be com- 

 posed of rounded cells with thickened walls ; 

 the bast fibres or liber. 



y. The cambium zone: granular-looking, and 

 composed of small angular thin-walled cells. 



8. The liber-layer: in cross section it seems 

 composed of rounded cells with much thick- 

 ened walls. Draw the section. 



3. Cut a transverse section through a node, and compare 

 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; 



