330 
HYMENOPHYLLACE^. 
SO long considered identical, as the two British Hymenophylla, 
we are bound to exercise the greatest caution, as well as candour. 
We must on no account draw our conclusions from mere appear- 
ances, — from isolated or ill-established facts, — or from assertions 
made either at random or by incompetent observers. I have 
peeled the matted rhizomata of these ferns from the rocks about 
Killarney, — have sat me down on the trunk of a fallen Arbutus, 
— have taken the mass of Hymenophyllum on my knees, and 
have carefully endeavoured to disentangle the tortuous wiry rhi- 
zomata of the two species. I have found every appearance in 
favor of the supposition that both forms of frond were produced 
by a single plant : the mat or carpet before me has appeared 
principally to consist of tunhridgense, but in every part rose the 
more erect fronds of Wilsoni, with their unilateral and secund 
pinnce : still the evidence of continuity between the rhizoma 
that produced one form, and that which produced another, was 
always wanting ; and on the same rhizoma, however carefully 
disentangled, I never found the two forms of frond. Candour 
also is essentially requisite : we must allow no theory, no previ- 
ously conceived idea, no dictum of the learned, to influence us 
in what is simply an enquiry after truth. The opinion of a Lin- 
neus, a Willdenow, or a John Smith, may raise, but cannot solve, 
a question of this kind. The test to which I have before had 
recourse — that of comparison in the most perfect or fruitful 
state — yields its evidence in favor of the two forms being dis- 
tinct as species. I have already observed that the great diffe- 
rence between them exists in the fructification, and I may also 
add that the more mature, the more perfect, the more fruitful the 
specimens, the greater are the discrepancies they exhibit, and the 
more decidedly and strikingly do they recede from each other. 
