CHAPTER VII. 



FERNWORTS AND SEED-PLANTS. 



Fernworts. 



Among the still more complex plants, the ferns and their 

 allies, the same "alternation of generatiotis " can be seen. 

 The two "generations," or phases, have, however, changed 

 much in relative size. Whereas in the liverworts and mosses 

 the gametophyte is much the larger and more conspicuous, 

 as well as the longer-lived, among fernworts the sexual phase 

 is so much smaller that it is seldom seen ; and in some 

 species it is almost microscopic. On the other hand, the 

 sporophyte is the phase which is usually 

 seen and the only part popularly known. 



63. The gametophyte. — The vege- 

 tative body of this phase of the fern- 

 worts in its best developed forms is a 

 small, flattened, green body of oblong, 

 orbicular, or cordate outline, commonly 

 less than half a centimeter in diameter, 

 rarely as much as 2 cm. (fig. 48). It 

 is strikingly like a thallose liverwort in 

 general form, being distinctly dorsiventral 

 and having rhizoids on its under side, 

 which fasten it in place. Only the central 

 part of the gametophyte consists of more 

 than one layer of cells. On the under 

 side of this central ' ' cushion, " as it is called, are borne the 

 sex organs. 



53 



Fig. 48,— Ventral side of 

 the gametophyte of a 

 fern, Aspleniutn, The 

 notched end is the an- 

 terior. Rhizoids near 

 posterior end. The small 

 circles show position of 

 male organs ; the chim- 

 ney-like projections near 

 anterior end the female 

 organs. Magnified jo 

 diam. — After Kerner. 



