MORPHOLOGY OF GYMNOSPERMS 



it is necessary to present briefly the vascular anatomy of the 

 pteridophytes, and especially that of the ferns. This will serve not 



only as an introduction to 

 Cycadofilicales, but also to 

 the vascular anatomv of 

 gymnosperms in general. 



VASCULAR ANATOMY OF 

 PTERIDOPHYTES 



The most important 

 recent advance in our 

 knowledge of the vascular 

 groups has been made by 

 the students of vascular 

 anatomy. Morphology had 

 become almost entirely re- 

 stricted to a study of the 

 structures associated with 

 reproduction, for these 

 structures seemed to offer 

 the only clue to the larger 

 relationships. An enor- 

 mous mass of facts had 

 been accumulated in refer- 

 ence to the anatomy of 

 the vegetative structures, 

 but it was not organized 

 so as to be of service to the 

 morphologist. Now vascu- 

 lar anatomy has emerged 

 as a subject organized upon a morphological basis, and its value in 

 supplementing the older morphology cannot be overestimated. In 

 fact, it is really the extension of morphology to include the vascular 

 system. 



The three conspicuous kinds of vascular axis among pteridophytes 

 are (i) the protostele (tig. 2), which is a single, solid, concentric vascu- 

 lar cylinder; (2) the siphonostele (fig. 3), which is a hollow vascular 



Fig. I. — Xeuropteris: impression of frond. — 

 From photograph by Kidston. 



