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- 
