365 
MUSCINE^. 
one side, and a row of smaller leaves upon the other side of the stem. The 
leaves are not branched, but entire or toothed, rarely slit. In some kinds peculiar 
outgrowths are formed upon the inner or upper surface of the leaves ; in Barbula 
abides articulated capitate hairs. The lamina, which in other cases expands 
right and left from the median plane, is, in Ftssidens, expanded in the median 
plane itself, proceeding from an almost sheathing base. The tissue of the leaf is, 
with the exception of the central vein, usually homogeneous and composed of 
cells containing chlorophyll, which sometimes project above the surface as mamillse ; 
in the Sphagnaceae and Leucobryum the tissue is differentiated into cells containing 
air, and others which contain sap and chlorophyll, arranged in a definite manner. 
The mode of branching of the stem of Mosses is apparently never dichotomous, 
but also probably never axillary, although connected with the leaves. Even when 
the branching is copious the number of lateral shoots is nevertheless usually much 
smaller than that of the leaves ; in many cases the lateral branches are definitely 
limited in their growth, leading sometimes to the formation of definite ramified 
systems similar to pinnate leaves {Thuidnwi, Hylocomiuni). When the primary 
shoot produces reproductive organs at the summit, a lateral shoot situated beneath 
it not unfrequently displays a more vigorous growth, continuing the vegetative 
system ; and by such innovations sympodia are formed. It sometimes happens 
that stolons, that is shoots either destitute of or furnished with very small leaves, 
creep on or beneath the surface of the ground, elevating themselves at a later period 
as erect leafy shoots. The mode of branching is very various, and is closely con- 
nected with the mode of life. The morphological origin of the lateral shoots has 
been carefully investigated by Leitgeb in the case of FoTitmalis and Sphagnum, and 
admirably described. Since these two genera belong to very different sections, the 
results obtained in this case may be considered as of general appHcation to the 
whole class. They agree in the fact that the mother-cell (which is at the same 
time the apical cell) of a branch originates beneath a leaf from the same segment 
as the leaf (Fig. ii6). In Fontinalis the branch arises beneath the median line 
of the leaf ; but in Sphagnum beneath its cathodal half. In consequence of the 
further development of the mother-shoot, the lateral shoot in Sphagnum appears at 
a later period to stand by the side of the margin of an older leaf; and this is 
probably the explanation of the earlier statement of Mettenius that in Neckera 
complanata, Hypnum triqueirum, Racomitrium canescens, and others, the lateral shoots 
stand by the side of the margins of the leaves. When the shoot arises beneath 
the median line of a leaf, and the leaves are arranged in straight rows, the further 
growth of the stem may cause it to seem as if the shoot originated above the 
median line of an older leaf, in other words as if it were axillary. Leitgeb states 
that articulated hairs arise in the genera named in the axils of the leaves, or perhaps 
more correctly at the base of the upper surface of the leaves. 
The dimensions attained by the leaf-bearing axes and axial systems of Mosses 
show a wide range. In the Phascaceae, Buxbaumia^ and others, the simple stem 
is scarcely i mm. in height ; in the largest species of Hypnum and Polytrichum 
it is not unfrequently 2, 3, or more decimetres in length, and, if belonging to 
more than one axis, even longer, owing to the formation of innovations and sympodia 
{Sphag?mm). The thickness of the stem is less variable ; jV "^'^^ smallest, 
