FILICES. (TRUE FERNS.) 441 



4. PELL .32 A, Link. CLIFF-BRAKE. 



Allied to Cheilanthes, from which it differs chiefly iu the continuous invo- 

 lucre and smooth fronds (without tomentum or scales), 



* Fronds herbaceous or sub-coriaceous ; veins clearly visible ; involucre broad and 



usually covering the sporangia till they are fully ripe. 



1. P. Breweri, Eaton. Rootstock short, densely covered with narrow ful- 

 vous chaff: fronds membranaceous, 2 to 6 inches long, simply pinnate with 

 mostly unequally 2-lobed pinnae. Proc. Am. Acad. vi. 555. From Colorado to 

 Utah and California. In clefts of rocks. 



2. P. gracilis, Hook. Rootstock very slender, creeping, nearly naked: 

 fronds very delicate, 2 to 4 inches long, oblong-ovate, pinnate with a few once 

 or twice pinnalifid pinnce ; segments oblong or obovate ; involucres broad and 

 delicate. From Colorado northward, eastward through British America, and 

 southward again into Iowa, Pennsylvania, etc. Crevices of damp and shaded 

 limestone rocks. 



* * Fronds subcoriaceous or coriaceous; veins rather obscure; involucre con- 



spicuous. 

 t- Pinnules obtuse, at least not mucronate : fronds 1 to 2-pinnate. 



3. P. atropurpurea, Fe'e. Frond 6 to 12 inches long, evergreen, nearly 

 smooth, ovate-lanceolate, usually bipinnate below, simpler upwards ; pinnules 

 oval to linear-oblong, ^ to 2 inches long. From Arizona and Alabama 

 northward to British America and Canada. Crevices of shaded limestone 

 rocks. 



- - Pinnules decidedly acute or mucronate. 



4. P. Wrightiana, Hook. Fronds 4 to 8 inches long, lanceolate to tri- 

 angular-ovate, bipinnate; pinnae longer than broad, having 3 to 13 oval or 

 oblong-oval pinnules, fertile ones with the margins rolled in to the midvein. 

 From Colorado and Arizona to W. Texas. Mostly in exposed rocky places, 

 especially in canons. 



5. P. densa, Hook. Fronds l to 2 inches long, ovate, closely tr ip innate ; 

 ultimate segments linear, 3 to 6 lines long, sessile, sterile ones serrated. In 

 California and Oregon ; also at Jackson's Lake, Wyoming ( Coulter). Clefts 

 of rocks. 



5. CRYPTOGKAMME, R. Brown. ROCK-BRAKE. 



Fronds rather small, and smooth, 2 to 4-pinnate, the fertile ones taller than 

 the sterile : stalks stramineous and tufted on a short rootstock. 



1. C. acrostichoides, R. Br. Fronds 2 to 4 inches long, chartaceous, 

 ovate, closely 2 to 4-pinnate ; pinnules ovate or obovate, adnate-decurrent, 

 those of the fertile fronds narrower and longer, the involucres very broad : sori 

 extending far down the veinlets. Allosorus acrostichoides, Spreng. From 

 California, Colorado, and Lake Superior, northward to Arctic America. In 

 dense patches among rocks. 



