FERNS 323 



O. sensibilis, Linn. Sensitive fern. Brake. Fig. 337. Sterile frond 

 triangular-ovate, the pinnae not extending quite to the midrib and toothed: 

 fertile frond usually lower than the other (1-2 ft. high), with a few pinnae. 

 Common in old pastures. 



O. Struthiopteris, Hoffm. Ostrich fern. Very tall (2-5 ft.), the 

 sterile fronds narrow, once-pinnate, with long-lanceolate acute-lobed 

 pinna;: fertile fronds much shorter, blackish, with many pinnae. 



3. POLYPODIUM. Polypody. 



Small ferns, with simple or once-pinnate fronds from slender creeping 

 rootstocks: sori round, borne at the ends of little veins. On dry cliffs. 



P. vulgare, Linn. Common polypody or polypode. Figs. 333, 334. 

 Fronds a foot or less tall, narrow-oblong in outline, pinnatifid, the lobes 

 nearly or quite entire: fertile pinnae not contracted. 



4. ADIANTUM. Maidenhair Fern. Fig. 336. 



Small ferns with compound forking fronds and wedge-shaped or some- 

 what triangular pinnae, shining stipes or petioles, and sori borne at the 

 ends of the veins under the reflexed margins of the pinnae. 



A. pedatum, Linn. Common maidenhair. Plant 2 ft. or less high, the 

 leaves forking into several or many long pinnae which bear broad pinnules 

 notched on the upper margin. Cool, shadj- woods. Very graceful. 



5. PTfiRIS. Brake. 



Coarse ferns of mostly dryish places, with long pinnae: sporangia borne 

 beneath the reflexed margin of the pinnules, on small, transverse veins. 



P. aquilina, Linn. Common brake. Figs. 139, 335. Fronds broadly 

 triangular, twice- or thrice-pinnate, the pinnules long-lanceolate, acuminate, 

 and lobed. Common in sunny places: perhaps our commonest fern. Two 

 to 3 ft. high, growing in patches, particularly in burned areas. 



6. ASPLF,NIUM. Spleenwort. 



Middle-sized ferns, mostly with pinnate leaves: sori oblong or linear, 

 borne on the upper side of a veinlet, or back to back on opposite sides of 

 the veinlet, these veinlets not interwoven. 



A. Filix-fcemina, Linn. Lady-fern. Large, the fronds 2-3 ft. tall, 

 growing many together, twice-pinnate, the pinnules oblong-pointed and 

 sharp-toothed: sori short and close together, at maturity becoming more 

 or less continuous. A very common fern in moist woods and copses. 



7. POLfSTICHUM. Christmas Fern. 



Much like the last in general appearance, but the sori circular and 

 covered with peltate indusia. 



P. acrostichoides, Kuntze {Aspidinm acrostichoides. Swartz). Christmas 

 fern. Figs. 331, 332. Fronds 2 ft. or less tall, narrow, once-pinnate, the 

 pinnae serrate and bearing a larger tooth on the upper side near the base, 

 the terminal part of the frond somewhat contracted in fruit. Common in 

 woods. Nearly or quite evergreen. 



