MOSS DEVELOPMENT. It 
rapidly-developed and consequently very short segments, forming 
mother-cells of leaves which at once grow out into expanded leaves 
instead of into filamentous structures. 
The apical cell of the stem is two-sided in Schistostega and 
Fissidens, in the rest of the Mosses it is a three-sided pyramid, with 
the basal surface turned upwards. 
Each segment of the apical cell arches outward and upwards, 
is cut off by a foliar wall, and developes by further divisions into a 
leaf, while the lower inner part of the segment produces part of 
the inner tissue of the stem. 
Since each segment forms a leaf, the spiral arrangement of the 
leaves, or Phyllotaxis, is determined by the position of the conse- 
cutive segments. 
In Fissidens two straight rows of alternate leaves are thus formed ; 
in Fontinalis three straight rows with the divergence }, the seg- 
ments themselves lying in three straight rows, because each newly 
formed primary wall is parallel to the last but three. 
In Polytrichum, Sphagnum, Andrezea, &c., on the other hand, 
each new primary wall encroaches on the ascending side with 
regard to the leaf spiral; the primary walls of each segment are 
therefore not parallel, and the segments themselves, when first 
formed, do not lie in three straight rows, but in three parallel spiral 
lines, winding round the axis of the stem, one above another. 
The angle of divergence of the consecutive segments, and their 
leaves, being greater than 3; the phyllotaxis is 2, 2, and so on; 
the apical cell giving the impression of rotation slowly on its axis 
while producing leaf-forming segments. 
The primary tissue (meristem) situated beneath the growing 
point of the stem is homogeneous and composed of cells with thin 
and smooth walls; all the cells are capable of division, and are 
rich in protoplasm, containing no coarse granules. ‘This tissue 
owes its origin, though not without exception, to the single mother- 
cell at the apex termed the apical cell. 
In passing over into permanent tissue, it becomes differentiated 
into an outer and an inner mass of tissue, not generally sharply 
defined. The cell walls of the outer are usually thickened, and 
of a bright red or yellowish colour; while the inner cells have 
broader cavities and thinner walls, slightly or not at all coloured. 
In many species of Grimmia, Funaria, Mnium, and Bryum, a 
central bundle of very thin-walled and very narrow cells is formed 
in addition to the outer and inner tissue; and in Polytrichum and 
Atrichum decided thickenings of the cell-walls take place in the 
central bundles in such a manner that each of several groups be- 
comes surrounded by a thick wall, and they together form a bun- 
dle ; doubtless these may be held to be fibro-vascular bundles of 
the simplest kind. 
