CORDAITALES AND GINKGOALES 



307 



elements of the secondary wood. This is well shown in Fig. 220. 

 Among the living conifers this condition is most nearly paralleled 

 by the Abietineae. 



The foliar trace 

 is of course of great 

 importance in this 

 as in other ancient 

 gy m n o s p erms . 

 Fig. 221 illustrates 

 the organization of 

 one of the bundles 

 of a broad cordai- 

 tean leaf (Cordaites 

 principalis) in both 

 transverse and 

 longitudinal section. 

 In a is shown the 

 transverse topog- 



\\ f fVi t r\ FIG. 217. Cordaitean wood from England 



and it is clear that the centripetal wood is well developed, ending 



upwardly in large 

 elements which are 

 pitted in their char- 

 acter. In the par- 

 ticular instance 

 figured there hap- 

 pens to be no devel- 

 opment of the 

 centrifugal xylem, so 

 that the phloem 

 abuts immediately 

 on the protoxylem. 

 With the flanks of 

 the metaxylem is 

 connected a zone of 

 narrow thick-walled 



FIG. 218. Cordaitean wood from Prince Edward Island elements which form 



