1 14 Salmon. — On the Genus Fissidens. 
necessary to follow the growth of the leaf-segment from 
its origin. 
The embryology of the leaf of Fissidens has been thoroughly 
investigated by Lorentz (9) and Leitgeb (10), and shows some 
extremely interesting developmental details, for the full 
account of which the works of these authors must be con- 
sulted. An important point to be noticed is that the first 
two divisions in the leaf-segment cut off cells which later 
form the vaginant laminae. The true leaf is thus indicated 
from the first — a fact which gives the strongest support 
to Robert Brown’s theory. 
The subsequent growth of the leaf-rudiment is very curious. 
The 2-sided apical cell, after giving rise to the two cells 
mentioned above, becomes altered in shape in such a way 
that the segments now cut off lie in a plane at right angles 
to that of the first segments, and so form the vertical part 
of the Fissidens leaf. No growth of the cells of the vaginant 
laminae takes place for some time, while the vertical out- 
growth continues to grow by the 2-sided apical cell in exactly 
the same manner as though it were a true leaf. 
This process of development is true only for those leaves 
of Fissidens which show a well-developed superior and inferior 
lamina ; in the case of the lower leaves, where the vertical 
outgrowth is small and chiefly terminal, the ‘ Drehung der 
Theilungsrichtung ’ of the apical cell takes place, as would 
be expected, only just before the conclusion of apical 
growth. 
Taking the embryology of the typical Fissidens leaf, how- 
ever, we have an instance of an interesting detail of develop- 
ment. The laminar outgrowth, which in the ancestral form 
of the leaf must have been merely a small wing at the back 
of the leaf, has here so increased in size and importance 
that it has assumed by its direct growth from the apical 
cell the character of a true leaf, while the rudiment of the 
latter, formed of the first two cells cut off, grows subsequently 
wholly by intercalary growth. The great effect which the 
abnormal structure of the leaf has on its embryology 
