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 Isoctales) 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 

 gametophj'tes (megagametophy tes) . 



2. Modern Ferns (Class Leptosporangiatae) 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 

 with an indusium. The mature spor- 

 angium (spore-case) in most common 

 ferns has a ring of thicker cells ex- 

 tending around it. When these be- 

 come (hy, they contract in such a way 

 „ ,^, ,, , as to break open the spore-case and 



Fig. 13o. — Modern ^ ^ 



ferns (sporangium and thus sct the sporcs free. Most Modcm 



son). '■ 



Ferns are terrestrial, and hence may 

 be set off as Land Ferns (Order Fili gales), in which 

 are the less common CHmbing Ferns (Lygodium), Tree 

 Ferns (FsunWy Cyatheaceae) , Filmy Ferns (Family //?//rteno- 

 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 (Polypodiiim vulgare), the Golden 

 Fern of California {Gymnograrnme triangularis), the 



