12 THE MICROSCOPICAL NEWS. 
The leaf originates from the swelling of a segment of the 
apical cell of the stem which is cut off by a wall. The lower part 
is concerned in the formation of the outer layers of tissue of the 
stem, and the apical part becomes the apical cell of the leaf. The 
formation of segments, which is limited, is in two rows to the right 
and left, and the tissue thus formed advances downwards, ceasing 
finally at the base. 
The whole of the tissue of the leaf in Fontinalis is a single layer 
of cells, but very commonly a vein, consisting of several layers of 
cells, is formed from the base of the apex. 
Often various forms of tissue become differentiated in the vein 
similar to the central bundles of the stem, and it is stated by 
Lorentz that the seta of the capsule is always provided with a simi- 
lar central bundle. 
The shape of the leaves of Mosses varies from almost circular 
through broadly lanceolate forms to the acicular, and are always 
sessile and broad at their insertion, usually densely crowded, only 
on the stolons of some species, the base of leafy shoots, and the 
pedicels of Aulacomnium and Tetraphis, do they remain small 
and remote. 
Round the reproductive organs they usually form dense rosettes 
or buds, and are termed the pericheetial leaves, not unfrequently 
assuming special forms and colours. 
The tissue of the leaf is usually homogeneous, and composed of 
cells containing chlorophyll, which sometimes project above the 
surface as mamille. In the Sphagnaceze and Leucobryum the 
tissue is differentiated into cells containing air, and others which 
contain sap and chlorophyll, arranged in a definite manner. ‘The 
cells of the Sphagnacez also contain special fibres, similar to the 
elators of the Hepaticze. 
The mode of branching of the stems of Moss is apparently never 
forked (dichotomous), but also probably never axillary, although 
connected with the leaves, and the number of lateral branches is 
