PERN FAMILT. 369 



midrib; dirisions very irameftms, nearly 1' long, somewhat scythe-shaped, 

 rather acute, serrate with incurved teeth ; fruit-dots very near the raidvein. 



A. crist&tum. Wet places in. woods, common; fronds narrowly. oblong, 

 l°-2° hi^h,,3f- 5' wide, rather rjgid, erect ;. pinnas triangular-ovate, broadest 

 at base, pinnatifid aJmost to the midrib, divisions not many, oblong, obtuse, 

 finely serrate, the largest ones sometimes toothed or pinnatifid-lobed ; fruit-dots 

 half-way between midvein and margin. — Var. CLiNxoNiXunM, in swampy 

 woods, N., is very much larger every way, with fruit-dots nearer the midvein, 

 and is often mistaken for A. Goldianum. — Var. PlokidAnhm, in wet woods 

 S., has the lower pinnse triangular-lanceolate and sterile, but the upper ones 

 fertile, narrower . and longer, with very short obtuse rather distant divisions, 

 which are decurrent on the winged secondary rhachis. 



■<- -t- fronds imperfectly evergreen, twice or thrice pinnate : the divisions cuty 

 toothed or indsed.: fruit-dots not near the margin: indusium rather small, 

 withering away. 



A. spinulbsum. Shady woods, very common N. : iVonds thin, oblong- 

 ovate ; pinnas oblong-lanceolate, the lower ones broader and somewhat triangu- 

 lar ; pinnules very numerous, oblong-ovate, pinnately incised, the oblong lobes 

 with spinulose teeth toward the ends ; indusium smooth or minutely glandular 

 at the margin. — Has several forms. — Var. dilatXtcm, in mountainous places, 

 N., is larger, broader in outline and commonly but twice pinnate ; pinnules of 

 the lowest pinnse greatly elongated. — Var. Bo6ttii, in swampy woods N., is 

 2° - 3° high, of narrow outline, barely twice pinnate, with oblong-ovate toothed 

 pinnules, or the lower ones pinnatifid : — it runs apparently into A. cristatum. 



■>- -I- -4- Fronds fully evergreen, thichish, about twice-pinnate : fruit-dots near the 



margin : indusium 'thichish, convex, persistent. 

 A. margindle. Rocky woods, common N. : fronds l°-2° long, ovate- 

 oblong, bluish-green, the stalk very chaffy ; pinnse lanceolate, 3' - 5' long ; 

 pinnules oblong, often curved, entire or obtusely toothed, attached by a broad 

 base to the narrowly winged secondary rhachis ; fruit-dots close to the margin, 

 rather large. 



§ 2. PoLTSTiCHUM. Indusium orbicular, peltate, attached by the centre to a 

 short stalk: veins forking, free: wild species of the couMry. 



A. acrosticholdes. Rocky woods, common ; fronds 1° - 2° high, grow- 

 ing in crowns, with chaffy rootstocks and stalks, evergreen, shining, lanceolat*!, 

 simply pinnate ; pinnse numerous, oblong-lanceolate from an unequal half- 

 halberd-shaped base, serrulate with bristle-pointed teeth, rarely incised, upper 

 ones of the fertile frond smaller and bearing copious soon confluent fruit-dots. 



§3. Ctrt6mium. Indusium as in § Polystichum. Fronds once pinnate : 



veins pinnate from the midrib, pinnately branching, the veinlels reticulated 



and forming arched meshes with 1 -3 /ree included veinlets rising from the 



base of the arch: exotic. 



A. fale&tum. Cult, from Japan: fronds 10-2° high, 5' -9' broad; base 



of stalk chaffy with large scales ; pinnse thick and shinina, end one large and 



rhomboid or halberd-shaped ; side ones few or many, oblong-ovate, long-pointed, 



nearly entire, lower side of base rounded, upper side angled or slightly auricled ; 



fruit-dots in many rows on all or nearly all the pinnse. 



16. CYSTCiPTERIS. (Greek for Bladder Fern, alluding to the thin, 

 sometimes inflated indusium.) Species few, mostly Northern. 

 C. fpAgiliS. Shaded or moist rocky places, common N, : fronds very deli- 

 cate, 4' -8' long, with slender stalks, oblong-ovate, twice-pinnate; pinnse with 

 a narrowly margined rhachis ; pinnules oblong or ovate, toothed or incised, very 

 variable ; indusium pointed at the upper end. 



C. bulbifera. Wet places, oftenest in ravines, from N. Carolina N. : 

 fronds l°-3° high, a' -5' wide at the base, narrowed above and much elon- 

 gated, twice pinnate, bearing scattered bulblets beneath ; pinnules oblong, ob- 

 tuse, toothed or pinnatifid ; indusium roundish, truncate on the upper side. 

 24 



