4 POLYPODIACEAE. 



4. PTERIDIUM. 



Large, mostly coarse ferns, with variously divided leaves; 

 fruit dots marginal, linear, continuous on a slender thread-like 

 receptacle which connects the tips of free veins; false indusium 

 membranous, formed of the reflexed margin of the leaf. 



Pteridium aquilinum pubescens Underw. Bracken or Brake. Root- 

 stock stout, black, subterranean, horizontally-creeping; petioles 30-120 cm. 

 high, erect, pale-green or straw-colored; leaf-blades 60-120 cm. long. 30-90 cm. 

 wide, glabrous above, pubescent beneath, ternate, the three branches each 

 bipinnate; ultimate segments oblong, acutish, mostly entire, the uppermost 

 coalescent, the lower more or less lobed. 



Common and difficult to eradicate from newly tilled land. In rich woods 

 this fern is sometimes eight feet tall. British Columbia to California and 

 Arizona. 



5. CRYPTOGRAMMA. 



Spore-cases on the back of the free forking veins, forming 

 oblong or roundish fruit-dots, which at length rim together 

 and cover the backs of the smallest subdivisions of the leaf; 

 indusium continuous, formed of the membranous somewhat 

 altered margin of the leaf, at first reflexed along the two sides 

 and meeting at the midrib, at length opening out flat. 



Margins of the fertile leaflets scarious, forming a false indus- 

 ium; ultimate segments of the sterile leaves linear-lanceo- 

 late, acute. C. densa. 



Margins of fertile leaflets not scarious; ultimate segments of 



the sterile leaves ovate, obtuse. C. acrostichoides. 



Cryptogramma densa (Brack.) Diels. (Pellaea densa (Brack.) Hook.) 

 Densely tufted, 10-20 cm. high; petioles dark brown, longer than the blades; 

 blades 3-6 cm. long, ovate or ovate-oblong, tripinnate; leaflets crowded, linear- 

 lanceolate, 6-12 mm. long, mucronate, entire on the fertile leaves, serrate on 

 the sterile ones. 



In rock crevices in the mountains, British Columbia to Montana and 

 California. Rare in our limits, Olympic Mountains, Clallam County, Wash- 

 ington, Elmer; Mt. Finlayson, British Columbia, Macoun. 



Cryptogramma acrostichoides R. Br. Stalks tufted, straw-colored; blades 

 of two sorts, the outer sterile ones on shorter stalks, the ovate or obovate 

 ultimate segments crenate or incised; the inner fertile ones long-stalked, the 

 ultimate segments elliptic or oblong, pod-like. 



Common among boulders at low elevations in the mountains, Alaska to 

 Lake Superior, Colorado and California. First collected by Menzies at 

 Nootka Sound. 



6. ADIANTUM. Maiden Hair Ferx. 



Fruit-dots marginal, short, covered by the reflexed portion 

 of the more or less altered margin of the leaf which bears spore- 

 cases on its under side from the tips of the free forking veins. 



Adiantum pedatum aleuticum Rupr. Maidenhair. Leafstalks dark 

 brown or black, polished, 30-40 cm. high; blades nearly circular, the principal 



