212 



BOTANICAL GAZETTE 



[SEPTEMBER 



the first cortical cylinder has decreased so much in its dimensions 

 that it is barely visible to the unaided eye. Furthermore, the 

 latter occurs, not as a continuous cylinder, but rather as a cortical 

 layer of separate, broad, and short bundles which are distinctly 

 collateral. The outermost cortical cylinder entirely disappeared 

 before reaching the height at which the section was taken. This 



m 



V V V" 



Fig. 2. — Cycas media: showing gross topography of transverse section of stem 

 near base; v, »', v", 3 distinct vascular cylinders; m, pith; It, leaf traces; lb, leaf 

 bases. 



Fig. 3. — Cycas media: showing gross topography of transverse section of stem 

 near tip; v, v', 2 vascular cylinders; m, pith; //, leaf traces; lb, leaf bases. 



quite agrees with Wordsell's (loc. cit.) account of a situation 

 exactly similar in Macrozamia. Fig. 1 represents the polyxylic 

 structure diagrammatically, as it might be seen in radial section in 

 the apical region of the stem. Differentiation which results in cor- 

 tical cambium begins farther from the stem apex in each succeed- 

 ing cylinder, being farthest in the outermost cylinder. 



