DEVELOPMENT OF THE SPOROGONIUM IN THE MOSSES. 27L 
can be best understood by a reference to the figures showing 
views of the whole theca (Pl. IX. figs. 1, 3, 4), and comparing 
them with the sections (Pl. IX. fig. 9, P1. X. fig. 18). P. formo- 
sum and P. juniperinum have an apophysis of symmetric hemi- 
spherical form (Pl. IX. fig. 5). 
The stomata are placed in a band in the annular depression 
or constriction separating the apophysis from the theca. 
The anatomy of the sporangium has been fully described by 
Lantzius Beninga (13), so there is only one point upon which 
I have made observations that need be mentioned. In Polytri- 
chum commune, and perhaps in some other species, the epidermis 
Was seen, upon a surface-view, to have a peculiar papillary appear- 
ance (Pl. XII. fig. 49). Sections vertical to the surface showed 
the cause of this: each epidermal cell rises at the middle point of 
its external surface, so as to form an outward projection from 
each cell, and from the cell-lumen a deep pit penetrates into this 
papilla, leaving the tip of the papilla only closed by a very thin 
membrane (fig. 48). 
This is the only pitting of any sort to be found throughout 
the moss-sporogonium, unless’ the thin parts of the cell-walls 
left between the thickenings of the teeth of the peristome 
be looked upon as pits. This peculiar modification of the 
epidermis is only found on the wall of the sporangium, and as 
that is the part covered by the calyptra it has occurred to me that 
a possible explanation of this structure is, that by means of these 
modified pits nourishment may be conveyed from the epidermal 
cells of the sporogonium to the calyptra. 
The apophysis is covered by a cuticularized epidern:is, with a 
distinct cuticle, in which, in a definite region, the stoma‘a are 
developed. These stomata, as Schimper (22) (23) pointed ut, 
are peculiar in tbat the stoma is guarded by what may, from one 
point of view, be regarded as a single guard-cell; for the cellulose 
plate separating the two cells is never completed to meet the 
side-walls of the mother-cell, thus leaving a passage at each end of 
the cellulose plate by means of which the cavities of the guard- 
cells communicate. There is, however, a nucleus on each side of 
the cellulose plate, which splits to form the stoma (Pl. X. 
fip. 17) The relations of the guard-cells are also shown in 
Pl. X. figs. 20-23, which show sections taken through the stoma 
at various points. 
My observations also confirm Haberlandt’s (6) in regard to 
