CHAPTER XXVII 
THE PTERIDOPHYTES 
360. Classes of Pteridophytes. — 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-plants. 
They are divided into 
Cuiass 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, which 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 whorls. 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 
