Wilson’s filmy fern. 
S20 
description of H. Wilsoni is from the pen of Sir W. Hooker. 
He describes it thus, ‘‘ Fronds rigid pinnate, pinnae recurved 
subunilateral wedge-shaped and 4 — 6 lobed, the segments linear 
undivided or bifid spinuloso-serrate, involucres axillary solitary 
ovate inflated entire, rachis only slightly margined towards the 
extremity ; ” * and he distinguishes it from H. tunhridgense in 
the following manner, More rigid and with larger reticulations 
than the last, quite distinct in its mode of growth, for all the 
pinnae are strongly curved backwards in a direction contrary to 
that of the fructification, the involucre is totally different larger 
browner of a more rigid texture truly ovate, each valve remark- 
ably convex for its whole length, the edges only of the valves 
being applied to each other, and they are quite entire.”f 
The roots and rhizoma of Wilsoni offer no characters by 
which 1 can .distinguish them from those of tunhridgense ; the 
fronds of both are circinate ; they make their appearance late 
in the summer months, and usually remain green through the 
winter, turning completely black in the ensuing spring. 
The frond consists of branched veins, clothed with a mem- 
branous wing, the margin of the wings being serrated : the wing 
on the main stem is less apparent in Wilsoni than in tunhrid- 
gense ; the pinnse are alv/ays convex above, while those of tun- 
hridgense are usually flat : Wilsoni has a more erect habit, 
tunhridgense a more horizontal, and, indeed, somewhat drooping, 
so that, on the trunk of a tree, the fronds seem to rest one on 
another like the tiles of a house. The involucre is very different 
from that of tunhridgense ; it is elongate, swollen at the base, 
and its exterior margin perfectly without serratures : when the 
capsules are mature, the involucre opens at the top, and, split- 
ting down the middle, remains widely gaping. 
A comparison of the two illustrations, which are drawn with 
considerable care, will enable the botanist to form a more cor- 
rect idea of the difference between them than I am able to 
convey by any description : they are of the natural size, the 
detached pinna of each being magnified. 
In treating of species so closely resembling each other, and 
* Brit. Flor. 446. 
t Id. 1. c. 
