xxvin] 



ANATOMICAL FEATURES 



33 



In the xylem portion of the bundle from the midrib of a forked 

 pinna of Cycas Micholitzii shown in fig. 400 the centrifugal xylem 

 elements are unusually numerous: the space between the two 

 xylems is occupied by parenchyma and the whole strand is enclosed 

 by a sheath of crystal-containing cells, s, with thick inner walls. 

 Fig. 400, 1 — 4, illustrates the gradual change in the form of the 

 bundle in the region of dichotomy^. The ground-tissue of the 



Fig. 400. Cycas Micholitzii. Vascular bundles in a forked] pinna ; px, proto- 

 xylem ; s, sheath of thick- walled ceUa ; cf, cp, centrifugal and centripetal xylem. 



petiole is abundantly supplied with secretory canals and in the 

 hypodermal region is a cylinder of stereome. In some petioles, 

 e.g. Macrozamia heteromera^, the ground-tissue cells are lignified 

 and reticulately pitted, a feature met with in some Mesozoic 

 cycadean leaves^. In Cycas media Worsdell noticed a tendency 



1 Seward (06). " Robertson (02). » geward (12^). 



s. in 3 



