45 . 
THE ONE-SIDED FILMY FERN. 
Hymenophyllum unilaterale. 
Plate 6 , Fig. 3 , Page 235 . 
The distinction between our two native Filmy Ferns was first 
noticed by Mr. W. Wilson, a botanist, and on this account 
the present species is frequently called by the specific name 
of Wilsoni. The term unilaterale, ‘one-sided,’ is, however, 
here retained as being a descriptive appellation. It has 
been stated that the range cf Unilaterale, throughout the 
world, is co-extensive with its near relative Tunbridgense. 
In the British Islands, however, though both are frequently 
found growing together in equal abundance — Tunbridgense 
in some localities being even the more plentiful of the two — 
Unilaterale has a somewhat wider distribution, especially in 
Scotland and Ireland. Both grow under the same, or 
similar, conditions, and these have been fully described in 
the case of Tunbridgense, in the preceding section. But 
Unilaterale is believed to prefer a situation higher with 
regard to the sea-level, and more exposed than Tunbridgense, 
a belief which, doubtless, finds proof in the fact that it is 
found growing alone at greater elevations. The same fact 
would appear to account for its greater abundance in 
Britain, though it does not satisfactorily dispose of the 
statement that the range of the two plants is co-extensive in 
other parts of the world. It may be suggested, however, 
that this particular statement is again open to question ; for 
