PTERIDOPHYTES 155 



cular structure, the Ophioglossales are more advanced than the majority 

 of pteridophytes. On the whole, the association is evidently with the 

 Filicales of the Marattia type. 



(6) Filicales 



General character. — The ferns constitute by far the largest group of 

 pteridophytes, including at least 3000 living species, and perhaps many 

 more. The group as a whole is very ancient, but most of the living 

 families are very modern. Two groups of Filicales are recognized : 

 Filicineae (true ferns), which are homosporous ; and Hydro pteridineae 

 (water ferns), which are heterosporous. 



(a) Filicineae 



General character. — Nearly all of the living ferns are true ferns. 

 They are well represented throughout the temperate regions, but are 

 especially abundant in the tropics. The sporophyte displays a great 

 variety of habits — ordinary terrestrial forms, epiphytes (perchers), 

 climbers, aquatics, and trees. Ferns are characterized generally by 

 their comparatively few, large, and usually branched leaves, which bear 

 numerous sporangia, usually upon the abaxial surface. The multipli- 

 cation of sporangia is thus facilitated, not by sporangiophore develop- 

 ment, but by distribution over a large leaf surface. 



Families. — In so large a group it is necessary to have in mind the 

 principal families. Disregarding the smaller families that have been 

 proposed, the following seven may be considered, conveniently but not 

 completely distinguished from one another by the character of the 

 annidus. The annulus is a group or band of thick-walled cells developed 

 in the wall of the sporangium and related to its dehiscence. 



1. Marattiaceae (ringless ferns). — Annulus wanting. About 25 

 tropical species in 5 genera. 



2. Osmundaceae (royal ferns). — Annulus rudimentary (fig. 366). 

 About 15 temperate and tropical species in 3 genera. 



3. Gleicheniaceae. — Annulus equatorial and indusium (see p. 165) 

 wanting (figs. 367, 368). About 25 tropical species in 2 genera. 



4. Hymenophyllaceae (filmy ferns). — Annulus equatorial and in- 

 dusium present (figs. 369, 370, 371). About 155 species, chiefly tropical, 

 in 2 genera. 



5. Schizaeaceae. — Annulus apical (figs. 372, 373, 374). About 95 

 species, chiefly tropical, in 4 genera. 



