VII. 



THE PTERIDOPHYTES. 



The plants of this subdivision approach the common 

 Flowering Plants in their structure much more nearly 

 than any thus far considered. 

 There is a marked differen- 

 tiation of tissues. True vas- 

 cular bundles give support 

 to the aerial stalks, and serve 

 to convey the fluids for the 

 nourishment of the plant. A 

 slight tendency to the forma- 

 tion of these differentiated 

 structures has already been 

 noted in the case of the stems 

 of Mosses, but no true vessels 

 are formed in them. From 

 this fact, that their structure 

 is wholly cellular, the plants 

 of the preceding subdivisions 

 are called cellular crypto- 

 gams. Because of the pos- 

 session of woody bundles, 

 and because one method of 

 reproduction is by spores and 

 not by seeds, the Pterido- 



FIG. 109. Pteris aqulhna. rh, rhi- 

 zome; ab, apical bud; I 1 , present 

 year's leaf; I 2 , withered leaf of 

 last year ; p, a pinna ; x, one of 

 the younger pinnae, which is seen 

 more highly magnified at B. 

 (After Sedgwick and Wilson.) 



phytes are called vascular 

 cryptogams. In the Ferns 

 and their allies fully developed fibrovascular bundles, 

 made up largely of spiral and scalariform vessels and 



183 



