CHAPTER XXI 
PTERIDOPHYTES (FERN PLANTS) 
209. Summary from Bryophytes. In introducing the Bryo- 
phytes a summary from the Thallophytes was given (see 
60), indicating certain important things which that group 
has contributed to the evolution of the plant kingdom. 
In introducing the Pteridophytes it is well to notice certain 
important additions made by the Bryophytes. 
(1) Alternation of generations. The great fact of alter- 
nating sexual (gametophyte) and sexless (sporophyte) gen- 
erations is first clearly expressed by the Bryophytes, although 
its beginnings are to be found among the Thallophytes. 
Each generation produces one kind of spore, from which is 
developed the other generation. 
(2) Gametophyte the chlorophyll generation. On account 
of this fact the food is chiefly manufactured by the gameto- 
phyte, which is therefore the more conspicuous generation. 
When a moss or a liverwort is spoken of, therefore, the 
gametophyte is usually referred to. 
(3) Gametophyte and sporophyte not independent. The 
sporophyte is mainly dependent upon the gametophyte for 
its nutrition, and remains attached to it, being commonly 
called the sporogonium, and its only function is to produce 
spores. 
(4) Differentiation of thallus into stem and leaves. 
This appears incompletely in the leafy Liverworts (Junger- 
mannia forms) and much more clearly in the erect and 
radial leafy branch (gametophore) of the Mosses. 
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