CORDAITALES AND GINKGOALES 



309 



pitted elements of the last-formed metaxylem. Below the pro- 

 toxylem lies the phloem, and still farther down the more elon- 

 gated and narrower elements of the inner transfusion sheath, which 

 in turn abut on the short, broad tracheary elements of the outer 

 transfusion sheath. At the very top lie other short transfusion 

 cells, and the inner elongated sheath in this region is absent as a 

 result of conditions which can readily be inferred from the in- 

 spection of the transverse view in a. There is some variety in 

 the development of the foliar bundles of the Cordaitales, but 

 all are characterized by the presence of well-marked centripetal 

 wood and a cordon of short tracheary elements, known as trans- 



P P* 



FIG. 220. Longitudinal view of cordaitean wood near the pith (after Scott) 



fusion cells, which are closely related to the centripetal or crypto- 

 gamic wood. 



The root in cordaitean forms, for reasons applying equally 

 to all Paleozoic gymnosperms, presents no features of special 

 interest beyond illustrating the general cordaitean organization 

 modified to the needs of root organs. 



It will be obvious from the statements made in the foregoing 

 paragraphs that there is clear evidence in the organization of 

 the foliar structures in the Cordaitales for their close affinity with 

 the Filicales, although naturally the degree of relationship is 

 much less intimate than that which characterizes the Cycadofili- 

 cales and even the Cycadales. Concerning the organization of 

 the microsporangia and seeds of the Cordaitales our knowledge 

 is unfortunately somewhat meager. The evidence in regard to 

 the microsporangium is not sufficiently definite to warrant an 

 opinion as to whether it was ectokinetic or endokinetic in its 



