BENNETTITALES 



45 



leaves are only once pinnate, and that in Williamsoniella coronata 

 the leaves are simple. 



In Williamsonia gigas the stem is outwardly unbranched and the 

 internal structure, judging from Williamson's reconstruction, would 

 also be unbranched. 



The stems were covered by an armor of persistent leaf bases, as in 

 most of the living Cycadales. The numerous axillary cones, often 

 hundreds, gave the stems a striking appearance. 



Fig. 38. — Williamsonia (Anomozamites) angustijolia: branching trunks with leaves 

 and strobili at the forks; about I natural size. — After Nathorst. 



The vascular system is an endarch siphonostele, the highest type 

 found in gymnosperms, and characteristic of the Archichlamydeae 

 and Sympetalae in the angiosperms. No seedlings have been ex- 

 amined and, consequently, it is not known whether a mesarch condi- 

 tion might be found, as in the living Cycadales. 



In transverse section the stem shows the large pith, scanty wood, 

 and thick cortex, which are so prevalent in the whole Cycadophyte 

 phylum (fig. 39). 



The scanty zone of wood, as in most of the living Cycads, shows 

 no growth-rings. Cycadeoidea jenneyana is exceptional in having a 



