FERN FAMILY. 369 



riRdrib; divisions very numerons, nearly 1' long, somewhat scythe-shaped, 

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



A. erist^tum. Wet places in woods, common: fronds narrowly oblong, 

 l°-2° high, 3' -5' wide, rather rigid, erect; pinnaj triangular-ovate, broadest 

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

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

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

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

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

 S., has the lower pinniB 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. 



■♦- •»- Fronds imperfertly evergreen, twice or thrice pinnate : the divlaions ciU- 

 toothcd or incised : fruit-dots not near the margin: indusium rather small, 

 withering away. 



A. spinulosum. Shady woods, very common N. : fronds thin, oblong- 

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

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

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

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

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

 the lowest pinnae greatly elongated. — Var. Boottii, 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. 



■»- -1- -t- Fronds fully evergref-n, thickish, about twice-pinnate : fruit-dots near the 

 margin : indusium thickish, convex, persistent. 



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

 oblong, bluish-green, the stalk very chaffy ; pinnie 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 margis, 

 rather large. 



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

 short stulk: veins forking, free : wild species of the country. 



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

 ing in crowns, with chaffy rootstocks and stalks, evergreen, shining, lanceolate, 

 simply pinnate ; pinna; 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. Cyrtomium. Indusium. as in § Poltstichum. Fronds once pinnate : 

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

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

 base of the arch : exotic. 



A. falektum. Cult, from Japan: fronds 1°- 2° high, 5' -9' broad; base 

 of stalk chaffy with large scales; pinnae thick and shining, end one large anA 

 rhomboid or halbcnl-shaped ; side ones few or many, oblong-ovatc, long-pointed, 

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

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



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

 sometimes inflated indusium.) Species few, mostly Northern. 



C. fr^gilis. Shaded or moist rocky places, common N. : fronds very deli- 

 cate, 4' -8' long, with slender stalks, oblong-ovate, twice-pinnate; j)innnB with 

 a luu-rowly 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, 3' -5' wide at the base, narrowed above and much elon- 

 gated, twice pinnate, bearing scattered bulblets beneath ; pinnules oblong, ol> 

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

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