Salmon. — On the Genus Fissidens. 
1 1 1 
laminae, although forming an insignificant part of the ‘ leaf, 5 
seem to be always present. 
The very few species (F. hyalinus , F. usambartcus , &c.) 
which, like F. dealbatus , possess rudimentary vaginant laminae, 
are extremely interesting in showing us the limit (as at present 
known) reached in the process of dwarfing the true leaf ; at 
the other end of the series we have species like F. bifrons 
(Schpr.), C. Mull., (Figs. 28, 29) and F. elamellosus, C. Mull, 
and Hpe , in which the appendage of the leaf is the insig- 
nificant part — -and between these extremes the other species 
arrange themselves in a perfectly continuous sequence. 
A point must be mentioned here, of which, I think, Bruch 
and Schimper have given an incorrect explanation. These 
authors, accepting Robert Brown’s theory, divide the leaf 
into four parts, viz. the two wings of the true leaf (i.e. the 
two vaginant laminae), the dorsal wing (ala dorsalis), borne 
at the back of the nerve of the vaginant laminae, and the 
vertical lamina (lamina verticalis), formed ‘ par la continuation 
d une des ailes foliares [vag. lam.] et par l’aile dorsale.’ 
I do not think the last-named part has arisen in this way, 
for the following reasons. In many species the areolation 
is not the same in the different parts of the 4 leaf,’ and the 
signification of this does not seem to have been noticed. 
F. floridanus , Lesq and James (Fig. 30) illustrates this 
feature well. Here the areolation of the vaginant laminae (b) 
is different to that of the superior and inferior laminae (a). 
The change in areolation occurs abruptly, and is seen most 
clearly in those species in which, as in F. floridanus , the 
vaginant laminae are unequal at their apex : there is then 
a distinct line from the apex of the inner vaginant lamina 
to the margin of the outer one (Fig. 30, x). 
This difference of areolation is not uncommon among the 
species of Fissidens (e. g. F. decipiens , De Not., F. lanceolatus , 
Hampe, &c.), and in all cases it is the superior and inferior 
laminae which show one kind of areolation, and the vaginant 
laminae the other, with an abrupt separating line, as shown 
at Fig. 31. The different structure of the cells on each side 
