77//'; rTKRIDOPHYTA 



32i 



another that they are sometimes regarded as three distinct divi- 

 sions, but their many points of resemblance make it perhaps more 

 satisfactory^ to group them together. 



Filicineae or Ferns. — ^This class, the largest of the three, 

 includes the most conspicuous and familiar of the pteridophytes. 

 The leaves, here known as fronds, are typically large and are 



Fig. 198. — A fern plant, the polypody {Polypodium vulgare). This is the 

 sporophyte generation. The stem is a creeping rootstock. On the backs of the 

 leaves are born sori, or clusters of sporangia. 



often deeply cut and dissected. The spores are all alike, 

 except in the small group of water-ferns where heterospory exists. 

 With a few exceptions, the gametophyte grows on the surface of 

 the soil and is provided with chlorophyll, thus existing as an 

 entirely independent plant. Three orders are recognized, the 

 Filicales, Ophioglossales, and Hydropteridales. 



1. Filicales or True Ferns (Figs. 198 and 199).— Almost all of 

 the ferns belong here, the other two orders being very small 

 ones. In our common species the stem is much reduced and is 



