-36- 



I have seen, also, the pinnae are alternate throughout, 

 which means that one pinna stands distinctly alone at the 

 base of the frond. The form was gathered on rocks on a 

 partly cleared hillside, July 8, 1904. at McCall's Ferry, 

 on the Susquehanna River in Pennsylvania, by Dr. C. E. 

 Waters. 



4. Forma platylobum Christ. This has a short and 

 rather broad frond with unusually broad pinnae, which 

 are rounded at the ends. In our American specimens 

 the pinnae are sensibly diminished in length at the base 

 of the frond, rendering it ovate in shape ; the sinuses 

 between the pinnae are sharp' thus bringing them close 

 together, and the sori are nearer to the costa than to the 

 edge. The terminal pirma is broad and blunt, very 

 often with three or four pairs of short, almost rotund 

 lobes at its base, and with the sori extending nearly to its 

 apex. The rootstock is uncommonly heavy for the size 

 of the fern. The only North American examples I have 

 seen came from Alaska, and were gathered by J. B. 

 Fleet of Tacoma, Wash., who reports the form as " grow- 

 ing everywhere " in Alaska. 



5. Yar rotundatum Milde. Fronds about 25 cm. long. 

 3 to 3-J cm. wide, stipe one-half the entire length of the 

 frond, Pinnae alternate throughout, fifteen to sixteen 

 on each side, regularly spaced between and very uniform 

 in length nearly to the tip, very round-ended. This is 

 one of the prettiest varieties of the species on account of 

 the regularity in all its features. Gathered by Dr. C. E. 

 Waters on rocks in dense woods at McCall's Ferry, Sus- 

 quehanna River. Pennsylvania ; Black Hills. South 

 Dakota (Dr. P. A. Rydbe'rg). 



GROUP II. 



6. Var. cambricum (L.) Willd. In this variety the 

 pinnae are broad and deeply lobed nearly down to their 

 costae, the three or four pairs of lower pinnae are much 

 contracted at their bases, the lowest pair being quite 



