Salmon . — On the Genus Fissidens. 109 
Lindberg and Muller ( 11 ) have rejected Robert Brown’s 
theory for the same reason. According to their interpretation 
of this theory, the inferior and superior laminae are a ‘ product 5 
of the nerve ; therefore, as nerveless species of Fissidens 
have been described, the theory fails to hold good. But 
even if we admitted that the outgrowth of these laminae was 
dependent on the presence of a nerve, we should hardly have 
reason to reject the theory. 
Four species have been described as nerveless — F. dealbatns , 
Hook. f. & Wils. ; F. hyalinus , Hook. f. & Wils. ; F. Metzgeria 
(C. Mull.), Par., and F. usambaricus , Broth. F. dealbatns (Fig. 
14) shows, in transverse section, cells which undoubtedly repre- 
sent a nerve. The cells are unthickened [as in species of 
Fissidens , belonging to the subgenus Conomitrium (see Fig. 
17)], and are more numerous near the base of the leaf, becoming 
less evident higher up (Fig 15), and ceasing just before the 
end of the vaginant laminae. F. hyalinus also shows the same 
trace of a nerve at the base of the leaves, but in this species 
the nerve dies out about halfway up the vaginant laminae. 
F. usambaricus has a group of about seven cells, which repre- 
sent the nerve (P"ig. 16). F. Metzgeria I have not been able 
to examine. 
There seems, however, no reason for considering the laminar 
outgrowth of the superior and inferior laminae as in any 
way connected with the nerve. If we examine the leaves 
of the other Mosses in which similar outgrowths occur, e. g. 
Polytrichum (Fig. 18), Catharinea (Fig. 19), Pottia (Fig. 20), 
Barbula (Fig. sr), and Tortida (Fig. 22), we find that in 
all cases the outgrowths spring from unthickened cells, similar 
to those of the lamina, and that the nerve can only be con- 
sidered as generally localizing the position of the outgrowths. 
In the nerveless leaves of some Hepaticae, too, we 
see very clearly the origin of laminar outgrowths from 
the ordinary cells of the leaf. Mitten ( 12 ) has pointed out 
that certain species of Schistochila ( Gottschea) and Micro- 
pterygium approach Fissidens in the shape of the leaf. Fig. 23 
represents the leaf of a species of Schistochila. These leaves 
