258 PHYLUM IX. PTERIDOPHYTA 
Marattias (Order MARATTIALES), large, very leafy ferns 
of the tropics, formerly abundant, now nearly extinct, 
and with them may be placed the aquatic Quillworts » 
(Order IsocraLEs) with slender rush-like leaves. The 
latter produce two kinds of spores, viz. microspores 
which are small, and megaspores which are much larger. 
The plants are thus heterosporous, in contrast with 
the preceding which are isosporous. The microspores 
produce minute antheridial gametophytes (microgame- 
tophytes), and the megaspores, larger archegonial 
gametophytes (megagametophytes). 
2. Modern Ferns (Class LEprospoRANGIATAE) develop 
their sporangia from superficial cells. 
461. These are our common ferns, and this class 
includes the greater part of the species now living. In 
them the sporangia are usually developed on the lower 
surface of the leaves in clusters (‘‘sori’’) of various shapes, 
and these may be naked or covered 
YE@ with an indusium. The mature spor- 
© ‘S® angium (spore-case) in most common 
ferns has a ring of thicker cells ex- 
<== tending around it. When these be- 
* es come dry, they contract in such a way 
ss age io aae pe: as to break open the spore-case and 
aninrd (sporangium and thus set the spores free. Most Modern 
Ferns are terrestrial, and hence may 
be set off as Land Ferns (Order Fiuicaugs), in which 
are the less common Climbing Ferns (Lygodium), Tree 
Ferns (Family Cyatheaceae), Filmy Ferns (Family Hymeno- 
phyllaceae), and Common Ferns (Family Polypodiaceae). 
In the last-named family nearly all of the ferns of our 
woodlands are found, including such species as the 
common Polypody (Polypodium vulgare), the Golden 
Fern of California (Gymnogramme triangularis), the 
