136 : Rhodora | Jury 
pody is a very variable species."! Discussion of the larger bearings 
of this difference, which the writer is considering in another paper, 
would lead us now too far afield; but the conclusion which immediately 
concerns us is, that the profound difference in the variability of the 
Polypodies of the two sides of the Atlantic, as well as on the two slopes 
of the North American continent, is due to the fact that they are two 
distinct species of quite different geological and geographic history 
and distribution. 
The diagnostic characters of the two species and their American 
variations are shown below. 
Rhizome firm, sweet, in American forms commonly 0.5-1 em. 
thick; its pale-cinnamon to castaneous scales uniformly 
colored (or darker toward the base), densely cellular, with 
thin cell-walls, peltately attached slightly above the 
base, 0.5-1 em. long; stipes (except in the smallest ex- 
tremes) 1-3 mm. in diameter, 0.2-3 dm. long: fronds 
0.2-5.5 dm. long, 0.1-2.4 (av. 1.1.) dm. broad: pinnae 
opposite, subopposite or alternate, the lowest com- 
monly shorter than the middle ones; the latter 0.2-2 
(in var. cambricum -4.5) em. broad, their midribs com- 
monly curving at base: sori commonly median........ 
Rhizome rather soft and spongy, not sweet, 2-7 mm. thick; 
its seales darkened on the back, loosely cellular, with 
thick cell-walls, cordate at base, often with a closed sinus, 
2-4.5 mm. long; stipes 0.6-1.7 mm. in diameter, 0.1-2 
dm. long: fronds 0.25-2.6 dm. long, 1.5-7 (av. 4) or in 
very unusual forms -11 em. broad: pinnae alternate, or 
the lowest subopposite, usually about as long as or 
. Slightly longer than the median; the latter 2-8 (in very 
unusual forms -11) mm. broad, their midribs and those 
of the upper pinnae straight: sori nearly marginal....2. P. virginianum. 
1. POLYPODIUM VULGARE L. Sp. Pl. ii. 1085 (1753). P. californicum 
Kaulf. Enum. 102 (1824). P. vulgare, var. Bong. Vég. Sitch. 175 
(1832). Marginaria californica (Kaulf.) Presl, Tent. Pterid. 188 
(1836). P. vulgare, y occidentale Hook. FI. Bor.-Am. ii. 258 (1840). 
P. intermedium Hook. & Arn. Bot. Beech. Voy. 405 (1841). P. 
falcatum Kellogg, Proc. Cal. Acad. i. 20 (1854). P. Glycyrrhiza D. C. 
Faton, Am. Journ. Sci., ser. 2, xxii. 138 (1856). Goniophlebium 
californicum (Kaulf.) Moore, Ind. Fil. 386 (1862). P. californicum, 
vars. Kaulfussii and intermedium (Hook. & Arn.) Ð. C. Eaton, 
Ferns N. A. i. 244 (1879). P. hesperium Maxon, Proc. Biol. Soc. 
Wash. xiii. 200 (1900). P. occidentale (Hook.) Maxon, Fern Bull. 
xii. 102 (1904).—Europe and adjacent Asia and north Africa; Atlantic 
Islands; Alaska to Lower California, Arizona and New Mexico. 
..l. P. vulgare. 
. D D Li D 
In North America the following varieties are recognizable, though 
! Britten, Europ. Ferns, 165 (1881). 
