POL YPODIA CE^. 79 



or covered when young with a membranous indusium which is 

 either a special outgrowth of the leaf or is formed from the 

 more or less altered leaf margin. Prothallium green, monoe- 

 cious or rarely dioecious. The family contains four-fifths of all 

 the ferns, comprising a hundred or more genera, of which 

 twenty-nine are represented within our limits. They may be 

 distinguished by the following 



ARTIFICIAL SYNOPSIS OF GENERA. 



1. Sporophyll closely rolled together, entirely unlike the sterile leaf, its segf- 



ments berry-like or necklace-like 20 



.Sori covered with indusja 2 



' Sori naked . . 3 



2. Sori marginal, covered with a reflexed portion of the leaf margin . . -lo 

 -, Sori dorsal or submarginal, provided with special indusia .... 14 



3. Sori spread in a stratum on the under surface of the leaf. 



I. ACROSTICHUM, p. 81 



Sori roundish, or not more than twice as long as broad 4 



Sori usually linear, always more than twice as long as broad ... 7 



4. Stipes articulated to the rootstock ; leaves (in our species) entire or simply 



pinnate 5 



Stipes not articulated to the rootstock ; leaves (in our species) bi — tripin- 

 natifid or ternate XXII. Phegopteris, p. 108 



5. Veinsfreeorunitingirregularly (often indistinct). II. Polypodium, p. 81 

 Veins copiously uniting (species sub-tropical) 6 



6.. Primary veins distinct to the edge, connected by parallel transverse 



veinlets IV. Campyloneurok, p. 83 



Areolae regular, each with two or more free veinlets bearing sori on their 



apices III. Phlebodium, p. 83 



Areolae copious, irregular with free veinlets spreading variously, 



V. Phymatodes, p. 84 



7. Leaves simple .... 8 



Leaves pinnate to quadripinnate 9 



8. -Leaves very narrow, grass-like ; veins indistinct, free. 



IX. VlTTARIA, p. 8g 

 Leaves broader; veins anastomosing . . VIII. Cheilogramma, p. 88 



9. Sori marginal, more or less confluent in a marginal band. 



VII. Nothol.«:na, p. 8s 

 Sori dorsal, following the veinlets, simple, forked, or pinnate. 



VI. Gymnopteris, p. 84 



