CHAPTER XXVII 



THE PTERIDOPHYTES 



360. Classes of Pteridoph3rtes. — This series of the ferns 

 and fern-like plants is, among other characteristics, distin- 

 guished from all other spore-plants by having much more 

 highly developed tissues. From the presence of vessels 

 the pteridophytes are often known as vascular spore-planis. 

 They are divided into 



Class 1. The ferns. 

 " 2. The horsetails. 

 " 3. The club-mosses. 



The distinctions between these classes are some of them 

 highly technical, but there are a few obvious characteristics 

 which may be briefly stated. 



The ferns have usually well-developed leaves, vs^hich are 

 often highly compound (Fig. 204). They are frequently 

 rolled up in the bud. Sometimes there are special spore- 

 bearing leaves, but usually the spores are borne on the 

 under surfaces of the ordinary foliage leaves. 



The horsetails have very small undivided leaves, ar, 

 ranged in vt^horls. The spores are borne on specialized 

 shield-shaped leaves, arranged in a sort of flower-like 

 cluster (Fig. 211). The branches are whorled. 



The club-mosses and their allies have mostly very small 

 and simple, often scale-like or needle-like, spirally arranged 



280 



