Salmon. — On the Genus Fissidens. 1 1 5 
tends to show that the abnormality must be of a remote 
origin. 
Reverting to the different theories put forward as to the 
morphology of the leaf of Fissidens , it is to be noticed that 
all authors have considered the structure as quite anomalous 
amongst Mosses, and no attempt has been made to seek 
for any connecting link between this and the* normal form 
of leaf of other Mosses. 
It seems to me, however, that there are two genera which 
clearly supply this link, and which, moreover, give additional 
reasons for the acceptance of Robert Brown’s theory. One 
of these genera is Bryoxiphium , Mitt. Here the leaves are 
of two shapes ; the barren stems have simple sheathing leaves 
(Fig. 41), with or without a narrow wing at the back of the 
nerve ; in the fertile stems the lower leaves are similar, but 
as they approach the apex the wing at the back of the nerve 
becomes broader, and the leaf becomes much longer, running 
out into a somewhat flexuose hair-like prolongation. Fig. 42 
shows a leaf from the region a little below the apex ; at 
the apex the prolongation often exceeds in length the rest 
of the leaf. 
The structure of these upper leaves is very curious. 
Bescherelle ( 17 ), who monographed the genus, thus describes 
them : — 4 La nervure est pourvue d’une aile dorsale tr&s 
etroite, presque nulle de la base au milieu et n’apparaissant 
souvent que vers le sommet de la feuille, ou elle se confond 
avec le prolongement d’un des cot^s du limbe foliaire pour 
former une lame speciale tres alongee, comme cela se voit 
dans les Octodicerasl 
If the sheathing part of the leaf really ended at the 
commencement of the prolongation, as Bescherelle states 
above, we should have practically the structure of a Fissidens 
leaf, but this is not the case. When the leaf is examined 
in surface view under the microscope, it can be seen by 
careful focussing that the wing on one side of the nerve 
in the prolongation is split to the apex. The side which 
is split is the one above the sheathing base, and is, in fact, 
