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 Hydropteridineae 
(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 
annulus. 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. 
