246 



PTERIDOPHYTA. 



[CH. 



main characters of the recent genus will enable the student to 

 appreciate the points of difference and agreement between the 

 extinct and present representatives of the Equisetales. 



Fig. 52. Equisetum maximum Lam. A. Fertile shoot with strobilus and 

 sterile leaf-sheaths [after Luerssen (89); slightly less than nat. size]. 



B. Sporophyll bearing open sporangia (after Luerssen ; slightly enlarged). 



C. Part of a transverse section (diagrammatic) ; v, vaUecular canals, e, en- 

 dodermis, u, carinal canals (after Luerssen; x20). D. Equisetum arvense 

 L. Part of a transverse section of an iuternode of a sterile shoot. 

 V, cortex, e, endodermis, x, xylem tracheids, a remains of annular tracheids 

 of the protoxylem, c, carinal canal (after Strasburger; x 90). 



Equisetuin. 



The plant consists of a perennial underground creeping 

 rhizome, branching into secondary rhizomes, divided into well- 

 marked nodes and internodes. From the nodes are given off 



