CHAPTER XLIX 



FERNS, CLUB MOSSES AND EQUISETUMS 

 (PTERIDOPHYTES) 



Superficially the ferns, club mosses, equisetums, and quill worts may ap- 

 pear much too diverse in form to be classified within one group, known 

 as the Pteridophytes (Gr. pteris, fern, and phyton, plant). The funda- 

 mental features of their life cycles, however, are quite similar, and are 

 sufiiciently unlike those of other groups of plants to warrant the con- 

 sideration of them as a single group. Altogether about 8000 species of 

 Pteridophvtes have been described and named, of which more than 7000 

 are ferns. 



During the Carboniferous Period, some 300 million years ago, the 

 forests were dominated by hundreds of tree species of Pteridophytes 

 ( Chap. LII ) . The coal deposits of Pennsylvania were formed primarily 



Fig. 305. Ferns (Polystichum miinitiim) often 4 feet in height in the moist forest 

 region of the northwestern states. Photo by W. S. Cooper. 



656 



