PTERIDOPHYTES 



99 



still use that name, although the sex-organs have been 

 found. 



The alternation of generations explains what was a mystery 

 to the older botanists. When the spore of a fern germinates, 

 it must produce a gametophyte (see 46, p. 77) . This gameto- 

 phyte is a minute green plant that looks like a very small and 

 delicate liverwort (Fig. 78, A). In fact, it is so small that 

 it is only seen by those who know where to look for it ; and 



FIG. 80. Antheridia of a fern : A, two antheridia, one containing sperms and the other 

 discharging them ; B, a single sperm, showing its coiled form and many cilia. 



it does not suggest a fern in the least. Although it is flat 

 and prostrate like a liverwort, unlike a liverwort it produces 

 the sex-organs (antheridia and archegonia) from the under 

 surface, against the moist substratum (Figs. 79 and 80). 

 This position is very favorable for the swimming of sperms, 

 for if there is moisture anywhere about the plant, it will be 

 found between the flat body and its substratum. The necks 

 of the archegonia also open on the under surface, so that 

 fertilization is favored in every way. 



The small gametophyte is large enough to produce sex- 

 organs, and it does not make food for the sporophyte, so that 



