THE VASCULAR CRYPTOGAMS 9 



of the anatomy of our native species, S. spinosa, which, 

 though exceptional in the genus, illustrates several points 

 of importance. 



In the upper part of the ascending branches the stem 

 has the structure shown in transverse section in Fig. 6. 



ep. 



FIG. 6. Selarjinella spinosa ; transverse section of stem, ep 

 epidermis ; en, trabeculae representing endodermis ; c, 

 external cortex ; st, stele ; the seven dark groups are proto- 

 xylem. Magnified about 35 diameters. (After Harvey 

 Gibson.) 



There is a single central cylinder traversing the 

 middle of the stem. This is surrounded by a 

 wide intercellular space, which is bridged over at 

 intervals by long radiating cells connecting the stele 

 with the cortex. The latter is thick and of ordinary 

 parenchymatous structure, and is bounded externally by 

 a large-celled epidermis without stomata. Now, returning 

 to the stele, we find the structure quite different from 

 anything which we have previously met with in a 



