3 io 



KEY TO THE GENERA. 



1 1 Indusium cup-shaped, fixed be- 

 neath the sorus ; sori minute on a 

 tooth of the ultimate pinnules ; 

 fronds very finely cut. Boulder 

 fern. DICKSONIA. 



229 



AcolopWrium 



Camptoaorus 



A*plnium 



d. Sori and indusium linear. 



1 1 1 Several times longer than 

 wide, double ; indusia opening 

 toward each other ; blade thick 

 linear, entire. Hart's-tongue. 



SCOLOPENDRIUM. 268 



1 1 1 Shorter, some parallel to the 

 midrib, others oblique to it, often in 

 pairs or joined at the ends, irregu- 

 larly scattered on the underside of 

 the frond ; blade tapering to a 

 slender tip. Walking fern. 



CAMPTOSORUS. 265 



1 1 1 Short, straight mostly oblique 

 to the midrib, indusium usually 

 narrow, opening toward the mid- 

 rib ; fronds lobed or variously 

 divided. Spleenworts. 



ASPLENIUM. 155 



f 1 1 Short ; indusium more or less 

 curved on the side attached to the 

 frond, and when young usually ex- 

 tending across a vein ; robust 

 species. Lady fern. ATHYRIUM. 180 



