426 PTERIDOPHYTES (FERN PLANTS) 



duces an enormous number of cells which go to form vegetative 

 tissues of various kinds, before sporogenous tissue is produced. 

 Thus by delaying the formation of sporogenous tissue, the sporo- 

 phyte of Pteridophytes has become more and more massive and 

 at the same time with its larger number of cells has formed more 

 kinds of tissues than occur in the sporophytes of Bryophytes. 

 It is the sporophyte, which is the plant that we call the Fern, 

 that is the conspicuous generation in the Pteridophytes. The 

 gametophytes in most cases are quite small and generally simpler 

 than the gametophytes of most Liverworts. In passing from the 

 Bryophytes, where the sporophyte is small, dependent, and rela- 

 tively simple, to the Pteridophytes, where the sporophyte is so 

 many times larger and differentiated into roots, stems, and leaves 

 so that it lives independently, one is struck with the big jump 

 between the two groups. In the absence of forms to bridge over 

 this gap, the relation between the Bryophytes and Pteridophytes 

 is obscure. The sporophyte with its roots, stem, and leaves is 

 now well advanced toward Seed Plants. 



Although the Pteridophytes are known as the Fern group, 

 there are many Pteridophytes, of which Horsetails and Club 

 Mosses are familiar ones, that are not really Ferns. The True 

 Ferns are the most highly specialized and much the largest group 

 of the Pteridophytes, but in order to get a notion of the most 

 important features contributed toward Seed Plants by Pterido- 

 phytes, a study of the Ferns should be followed by a study of 

 some other groups of Pteridophytes. 



Filicales 



The Filicales are composed of the True Ferns and the Water 

 Ferns. The latter are small forms living in the water or mud and 

 are supposed to be an aquatic branch of the True Ferns. Al- 

 though the Water Ferns present some features of interest to 

 special morphologists, they will receive no attention in this brief 

 discussion. The True Ferns, which are the most abundant and 

 familiar of all Pteridophytes, are even more abundant in the 

 tropics than in the temperate regions. In the tropics the sporo- 

 phytes of some grow so large as to be called Tree Ferns. 



Sporophyte. Since the gametophyte is very inconspicuous, 

 the sporophyte, or the plant known as the Fern, is the only genera- 



