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 



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

 near base; v, v', v", 3 distinct vascular cylinders; m, pith; //, leaf traces; Ih, leaf 

 bases. 



V V 



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

 near tip; v, v\ 2 vascular cylinders; /«, pith; //, leaf traces; Ih, leaf bases. 



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

 exactly similar in Macrozamia. Fig. i 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 cyhnder. 



