1 1 6 Salmon . — On the Genus Fissidens. 
a direct upward growth of the whole of the true leaf. This 
is seen at once in a transverse section of the leaf near the 
apex (Fig. 43). 
The structure of the leaf is not therefore so closely similar 
to that of Fissidens as Bescherelle asserts, but the genus 
Bryoxiphium is, nevertheless, very interesting in showing 
us the first start, so to speak, of a Moss with sheathing, 
horizontally inserted leaves, arranged distichously, producing 
a vertical expansion, in the shape of a wing at the back of 
the nerve. This wing, in the upper leaves, is prolonged 
upwards for a considerable distance, occupying one side 
of the nerve, while on the other side the true leaf has grown 
upwards from the sheathing base in the form of two narrow, 
vertically compressed wings. 
The nerve-structure of Bryoxiphium is of interest in com- 
parison with that of Fissidens. Fig. 44 is a section at the 
base of the leaf, where there is no dorsal wing ; Fig. 45, 
where the wing is well developed. In the latter section we 
see that the presence of the wing has scarcely interfered with 
what may be considered the original structure of the nerve. 
There are, however, often a few unthickened cells beginning 
to grow through the stereid band in the direction of the 
dorsal wing ; sometimes we find a row of these cells running 
obliquely right through, and in such cases we have a clear 
indication of the ‘ conjunctivae ’ which form so distinctive 
a feature of the Fissidens nerve. 
The other genus is Sorapilla , Spruce and Mitt. : Fig. 46 
shows the leaf of the single species S'. Sprucei , Mitt. We 
see here at once a close resemblance to the leaf of Fissidens ; 
also, that as compared with the typical form of the latter 
(Fig. 1), the relative size of the different parts of the leaf 
is reversed. The sheathing part of the Sorapilla leaf is seen 
obviously to be the true leaf, and forms by far the greater 
part of the expansion, and the vertical outgrowth from it, 
corresponding to the inferior and superior laminae, is insig- 
nificant in comparison. Figs. 48-52 show the nerve-structure. 
The nerve throughout is ill-defined, and consists of only 
