96 



MORPHOLOGY OF GYMNOSPERMS 



one another through the foliar gaps. The presence of foliar gaps 

 is an evidence of fern connection, and this is confirmed by the usual 

 occurrence of mesarch bundles and sometimes of concentric bundles 

 in all regions of the vascular system outside of the primary cylinder. 

 If such bundles as occur in leaf traces, leaves, peduncles, and cotyle- 

 dons, were present in the primary cylinder, it would correspond 

 to that of Lyginodendron, which is that of Filicales except for the 

 secondary wood. 



Fig. 73. — Zamia floridana: transverse section of stem, showing the large pith, 

 rather narrow zone of xylem and phloem, and the thick cortex traversed in various 

 directions by oblique sections of the leaf traces (girdles); about natural size. — After 

 Coulter (75). 



A historical r&um^ of the development of knowledge in reference 

 to the vascular anatomy of the stem of Cycadales has been published 

 by WoRSDELL (20), from which the following facts are obtained. 

 In 1829 Brongniart (i) described the stem of Cycas revoluia, re- 

 futing the idea that cycadean stems are similar to those of monocotyle- 

 dons. In 1832 Von Mohx (2) investigated Cycas and Encephalartos, 

 discovering in a species of the latter genus the meshwork of vascular 



