26 FERN FAMILY 



A. Sori without indnsia. 

 Backs of fronds without powder. 



Fronds simply pinnate 1. Polypodium. 



Fronds at least 2-pinnate; high altitudes 2. Phegopteris. 



Backs of fronds with whitish or yellowish powder 3. Gymnogramma. 



B. Sori witli indusia. 



Sori marginal, covered by the altered reflexed margin of 

 the frond. 

 Stalks light or straw-colored (except at base). 



Fronds of 2 sorts, fertile and sterile, differing in 



appearance 8. Cryptogramma. 



Fronds all alike 5. Pteris. 



Stalks dark-colored. 



Fronds and stalks either scaly or woolly or both; 

 indusia separate, or if continuous the segments 



bead-like 6. Cheilanthes. 



Fronds and stalks neither scaly nor woolly. 



Indusium not continuous, bearing sporangia on its 

 under surface; segments thin; midvein not 



medial, sometimes wanting; damp places *• Adiantum. 



Indusium continuous, the sporangia on the surface 

 of the frond; segments thick (except P. brew- 

 eri)\ midvein medial; dry exposed places... '« Pellaea. 

 Sori not marginal, each covered with a special indusium. 

 Sori round. 



Indusium scale-like, attached to the vein below the 



sporangia !3- Cystopteris. 



Indusium saucer-like or fringe-like, inferior, i. e., 

 attached centrally to the stalk beneath the spo- 

 rangia 14 - WOODSIA. 



Indusium shield-shaped, superior, i. e., attached cen- 

 trally to the stalk above the sporangia. 



Indusium orbicular, without a sinus U« Polystickum. 



Indusium kidney-shaped, or if orbicular then with 



a narrow sinus 12. Aspidium. 



Sori oblong; tall ferns. 



Segments of frond cut-toothed; sori oblique to the 



midribs 10. Asplenium. 



Segments of frond not cut-toothed; sori parallel to 



the midribs 9. Woodwakdia. 



1. POLYPODIUM. 

 1. P. vulgare L. Common Polypody. Stalks 2 to 8 in. long, 

 slender, firm, erect, naked. Fronds smooth, 4 to 12 in. long, 

 1 to 4 in. broad at base, ovate-oblong or oblong-linear, cut to 

 or nearly to the rachis into entire or toothed oblong-linear 

 acute or obtuse segments. Sori large, round, usually in one 

 row midway between the margin and midrib, without indusia. 

 Veins free, with 3 or 4 veinlets having thickened ends, the 

 lowest veinlet on the upper side of the vein bearing a sorus 

 at its end. 



