io8 Salmon. — On the Genus Fissidens. 
Continuing with F. fasciculatus , Fig. 9 needs some explana- 
tion. The bistratose portion between the vaginant laminae 
and the nerve is not to be considered as formed by the 
union of the two laminae, but is the beginning of the superior 
lamina. Fig. 10 shows the apex of the vaginant laminae, 
which are here, as is usually the case, unequal above. Section 
11 is taken above the vaginant laminae, through the inferior 
and superior laminae, which are bistratose in this species. 
Those species of Fissidens which, like F. fasciculatus , Hsch., 
F. linealis , Bryol. eur.. &c., possess dorsal and ventral stereid 
bands, afford a clear proof of the horizontal insertion of the 
leaves, and the nerve-structure at the base of their leaves 
is quite irreconcilable with the theories that require a vertical 
insertion. These species are valuable in distinguishing for 
us so clearly, by means of the dorsal and ventral stereid 
bands, the under and upper surfaces of the true leaf: but 
we find, generally, among the rest of the species of Fissidens , 
a nerve-structure giving the same evidence. We often see, 
as in Fig. 1 2, a clear indication of a dorsal band, in the form 
of two principal groups, almost connected by small scattered 
groups of stereid cells. Moreover, in the large number of 
species examined, I have always found that, at the base 
of the leaf, even in those cases where the inferior lamina 
still existed, the two stereid bands approached each other 
towards the back of the leaf (vaginant laminae), indicating 
clearly a concavo-convex nerve. 
The symmetry of the leaf, too, as seen in transverse section 
across the lower part, is all against Lindberg’s theory of a 
‘ stipule ’ having become adnate to the nerve — it can at once 
be seen, e.g. in Figs. 2 and 3, that it is not the presence of 
one of the vaginant laminae, but that of the inferior lamina, 
which makes the leaf irregular. Neither Lindberg’s ‘stipule’ 
theory, nor the earlier one of the ‘ split leaf,’ has any special 
evidence to support it ; while Robert Brown’s theory so 
admirably accounts for the internal structure of the leaf, that 
it may, I think, be safely accepted, provided that the objections 
that have been raised against it can be shown to be groundless. 
