78 ELEMENTARY BIOLOGY. [VIII. 



tinuous, being interrupted by the cambium zone 

 (//) 



/. 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. 



/3. The small thick-walled wood-cells, wedged in 

 between the vessels. 



7. 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 thickened 

 walls. Draw the section. 



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

 it with that through the internode. 



o 



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; 

 working from the medullary cavity outwards, note the 

 following layers, using at first a low power. 



a. The pith-cells: much as in the transverse sec- 

 tion. 



b. The spiral vessels : elongated tubes with a spiral 

 thickening on their walls. 



c. The wood-cells : elongated and with much thick- 

 ened walls. 



d. The dotted ducts: much like b, but the thickening 

 not deposited in the form of a spiral. 



