CHAPTER XV 



PHYLUM IX. PTERIDOPHYTA* 

 THE FERNS 



449. The Ferns are green plants that as to their 

 gametophytes are of smaller size than the Mossworts, 

 while, as to their sporophytes they are much larger and 

 more complex. In fact the gametophyte generation is 

 so small compared with the sporophyte that it is usually 

 overlooked, or when seen is often not recognized as a 

 fern at all by those who are not familiar with the whole 

 life cycle of these plants. The fern that we commonly 

 see with its roots, solid stems, and ample leaves is the 

 sporophyte generation, which has become so large and 

 conspicuous in this phylum that it completely over- 

 shadows the little gametophyte. 



450. The gametophyte (commonly called the "pro- 



thallium") is usually a flat thallus, of 

 one or more layers of nearly uniform 

 chlorophyll-bearing cells, the whole 

 being rounded or heart-shaped in out- 

 line. Its longitudinal axis is consider- 

 ably thickened, and this portion is pro- 

 vided underneath with many root-hairs, 



intermingled with which in most cases are the antherids 



and the archegones. 



451. The antherids are nearly globular, few-celled 



* This name is here used in the narrower sense excluding Cala- 

 mites and Lycopods. 



254 



