THE FERNS 



309 



The material of this chapter will be treated under the 

 following headings: 



Class I. The ferns, or Filicinece. 



Class II. The horsetails, or Equisetinece. 



Class III. The club mosses, or Lycopodinece. 



Fossil plants and coal. 



The origin and evolution of the pteridophytes. 



Summary of the pteridophytes and their advances over the bryophytes. 



CLASS I. THE FERNS, OR FILICINE^ 



304. The ferns. The ferns are a very large assemblage of 

 more than four thousand species, and most of them can be 

 recognized at a glance by 

 the characteristic forms of 

 their leaves, called fronds, 

 and by their habits of 

 growth. They are widely 

 distributed, but reach their 

 greatest luxuriance in the 



ipics, where they present 



me very striking dis- 

 ilays. Thus the tree ferns 

 have stems thirty or forty 

 feet high, with a crown of 

 fronds often fifteen or more 

 feet in length. The stems 

 of some of the tree ferns 

 are covered by a sheath of 

 fibrous roots (as in Dick- 

 sonia, Plate VII), and in 

 Other types the bases of FlG 2 72. The stag-horn fern (Platycerium 

 the old and withered fronds Willinki) 



form a Similar investment. A tropical epiphytic fern with two forms of 



Thereare also in the tropics ]f> t ne ? f t which grows closely against 



the bark of trees and gathers and holds 

 Certain small delicate ferns moisture and humus. After Goebel 



