18 
PLANTS OF YELLOWSTONE NATIONAL PARK 
4. Spore cases not marginal. Lady-fern (Athyrium ftlix-femina )-(p. 19) 
5. Rootstocks slender, creeping; fronds delicate, lax, the stipes very slender; 
blades membranous, the segments smooth. Brittle fern (Filiw 
fragilis) ------_____ (p. 19) 
5. Rootstocks massive; fronds firm, erect, the stipes stout, appearing inflated; 
blades herbaceous, glandular, hairy beneath. Rocky Mountain woodsia 
(Woodsia scopulina) —_____________(p. 19) 
American rockbrake (Cryptogramma acrostichoides),—A. small, 
alpine fern of rocky situations. Rootstocks in massive tufts. Fronds 
numerous, closely clustered, of two kinds, the fertile ones 4 to 7 
inches long, long-stalked and much surpassing the spreading sterile 
ones. Blades of sterile fronds ovate, 2 to 3 times pinnate; fertile 
blades simpler, with linear-oblong segments. 
American maidenhair (Adiantum pedatum ).—A delicate, graceful 
fern of moist, rocky woods and ravines. The rootstock is short- 
Figure 1. —Bracken. Photograph by A. R. Figure 2. —Brittle fern. Photograph by 
Sweetser. A. R. Sweetser. 
creeping. The erect fronds are 9 to 40 inches long with purplish- 
brown, polished stipes. The blade is roundish in outline, the nu¬ 
merous linear divisions arising from the upper side of 2 equal 
branches; segments close, oblong, deeply cleft on the upper side. 
Rare in the park. 
Western bracken (Pteridium aquilinum var. pubescens ).—A coarse 
fern of open or partially shaded, acid-soil situations, usually geyser- 
ite in the park. The slender, woody, freely-branched rhizome is 
