WILSON'S FILM FERN. 309 
part, and there forming a narrow wing to the rachis, distinct below ; 
curved backwards, subunilateral, wedge-shaped in circumscription, 
digitately pinnatifid, 7. e. two or three times dichotomously forked, 
without an axial vein, the segments developed on the anterior side. 
Ultimate segments linear, obtuse, spinulosely serrate. The fronds 
when luxuriant have a tendency to become branched. 
Venation consisting of two or three dichotomous ramifications of 
the wiry ribs, which branch alternately from the main rachis; each 
ultimate segment having one of these ribs or veins along its centre, 
not quite reaching to the apex. 
Fructification produced on the upper parts of each annual growth, 
extra-marginal and supra-axillary as in the former species. Sori 
consisting of numerous spore-cases, clustered around the short 
receptacle, on which they are sessile. Receptacle free, central, 
spongy, oblong club-shaped, shorter than the valves of the invo- 
lucre. Involucres supra-axillary, more or less obviously stalked, 
curved forwards, i. e. in a direction opposite to that of the segments, 
inflated, two-valved, the valves ovate-oblong, strongly convex, and 
quite entire at the edges, which are at first closed, but at length 
become gaping. Spore-cases sessile, vertically compressed, thus 
lenticular, obliquely affixed. Spores minute, irregularly triangular. In 
some instances, especially where the frond becomes branched at the 
apex, numerous sori are borne without order on the segments, but 
usually they are confined to one on each pinna, next the rachis. 
Duration. The rhizome is perennial. The fronds are perennial, 
enduring for two or three years, or more, renewing their growth 
annually, as in the well-known case of Lycopodium annotinum. 
We are indebted to Mr. F. Clowes, of Windermere, for the 
interesting observation that the fronds of this species of Hymeno- 
Phyllum resume their growth after the first year, unlike those of 
H. tunbridgense, which complete their growth in one season. Mr. 
Clowes obligingly communicated for our folio edition (in 1856), 
the following note of his observations :—“I have a large plant of 
H. tunbridgense and of H. unilaterale, which were put into a case 
in March, 1854. Both are growing vigorously; but I remark 
that all the fronds of H. tunbridgense are annual—I mean, they 

