vii PTERIDOPHYTAFILI-CINE&.OPHIOGLOSSACE& 233 

 CLASS I. FILICINE^E (FILICALES) 



The Filicinese or Filicales, as already stated, include by far 

 the greater number of existing Pteridophytes, and are much 

 more extended in range and abundant in numbers than either of 

 the other classes. A marked characteristic of all Ferns is the 

 large size of the leaves, which are also extremely complicated 

 in form in many of them. In a few of these the leaves are 

 simple, e. g., Ophioglossum, Vittaria, Pilularia, but more com- 

 monly they are pinnately compound and sometimes of enormous 

 size. The stem varies a good deal in form and may be very 

 short and completely subterranean, as in species of Ophioglos- 

 sum and Botrychium, or it may be a creeping rhizome, or in 

 some of the large tropical Ferns it is upright, and grows to a 

 height of 8 to 10 metres, or even more. 



While some forms of the Ferns are found adapted to almost 

 all situations, most of them are- moisture-loving plants, and 

 reach their greatest development in the damp mountain forests 

 of the tropics. A few, e. g., Ceratoptcris, Azolla, are genuine 

 aquatics, and still others, e. g., species of Gymnogramme, live 

 where they become absolutely dried up for several months each 

 year. These latter will quickly revive, however, as soon as 

 placed in water, and begin to grow at once. In the tropical 

 and semi-tropical regions many Ferns are epiphytes, and form 

 a most striking feature of the forest vegetation. With few ex- 

 ceptions the sporophyte is long-lived, but a few species are 

 annual, e. g., Ceratopteris, and depend mainly upon the spores 

 for carrying the plant through from one season to another. 

 The sporophyte may give rise to others by simply branching in 

 the ordinary way, or special buds may be developed either from 

 the stem or upon the leaves (Cystopteris bulbifera). 



Besides the normal production of the garnetophyte from 

 the spore, it may arise in various ways directly from the 

 sporophyte (apospory) ; and conversely the latter may develop 

 as a bud from the garnetophyte without the intervention of the 

 sexual organs (apogamy). 



The Filicineae include both eusporangiate and leptospo- 

 rangiate forms, indeed the latter occur only here. The former 

 comprise the homosporous orders, Ophioglossales and Maratti- 

 ales, and possibly the heterosporous order Isoetales, whose sys- 

 tematic position, however, it must be said is still doubtful. The 



