CHAPTER VIII 



PTERIDOPHTTA — Concluded 



Beside the true ferns there are two other classes of 

 existing Pteridophytes, — the Equisetinese, (horsetails, 

 scouring-rushes) and the Lyeopodinese or club-mosses. 



The former, while showing certain points of resem- 

 blance to the ferns, still differ so widely from them that 

 they are properly included in a separate class. All the 

 known living forms belong to a single genus, Equise- 

 tum, which comprises about twenty-five species, mostly 

 belonging to the northern hemisphere, and especially 

 well represented in the United States. The peculiar 

 sporophyte (Fig. 36, A), with its jointed, grooved stems, 

 and sporiferous cones, is familiar to every botanist. 



The gametophyte is less generally known and shows 

 many points of resemblance to that of the ferns, espe- 

 cially the Eusporangiatse. The green spores germinate 

 promptly if sown as soon as they ripen, but soon lose 

 their power of germination. After about a month the 

 male gametophyte is mature, the female plant requir- 

 ing a somewhat longer time. In its earlier stages the 

 gametophyte is much like that of the common ferns, 

 but is more irregular in shape, developing more or less 

 definite lobes, which are especially conspicuous in the 

 female plant. The growth of the latter is a good deal 

 like that of the gametophyte of Maraltia or Osmunda, 



139 



