MUSCI, 
381 
very short seta of the sporogoniiim swells, as in Sphagnum and Hepaticx ; the 
roundish theca ruptures the calyptra laterally, without raising it up as a cap. Archidium 
agrees with the true Mosses in the formation in the theca of an intercellular space 
running parallel to its lateral surface, which separates the wall from the inner mass 
of tissue. The latter appears as a column continuous at the base and apex with the 
wall of the theca. But while in the true Mosses a layer of cells parallel to this inter- 
cellular space produces the spore -mother -cells, it is here only a single cell lying 
eccentrically in the inner mass of tissue that becomes the primary mother-cell of all 
the spores (Fig. 264, A). It grows considerably, and supplants the other cells, until 
it lies free in the hollow of the theca; it then divides into four cells, each of which 
produces four spores. The wall of the primary mother-cell remains entire, while the 
sixteen spores grow, and fill up the whole of the theca, the inner cell-layer of which 
is also absorbed (Fig. 265). 
4. In the BryacesB or True Mosses the sporogonium is always stalked, and the 
seta is usually of considerable length. The seta is cylindrical, obtusely pointed 
below, and firmly implanted in the vaginula; the theca always opens by the de- 
tachment of its upper part as a lid {Operculum) ; the operculum is either simply and 
smoothly detached from the lower part of the theca, or a layer of epidermal cells 
termed the Annulus is thrown off" in consequence of the swelling of their inner walls, 
and the operculum in this way separated from the theca. Most commonly, after the 
operculum has fallen off", the margin of the theca appears furnished with appendages 
of very regular and elegant form arranged in one or two rows ; the separate append- 
ages are termed Teeth or CUia, the whole together the Peristome; if the peristome is 
wanting, the theca is said to be gymnostomous. The theca is at first a solid homo- 
geneous mass of tissue ; the differentiation of its interior begins with the formation of 
an annular intercellular space which separates off" the wall of the theca consisting of 
several layers of cells ; but the wall remains attached above and below to the colu- 
cells of the spores are not derived from a single primary cell. A variable number of spore-mother- 
cells (1-7) are developed independently, each of which gives rise to four spores. They are arranged 
quite irregularly. 
Fig. 266. — Fimaria hygro7netrica ; A young leafy plants 
with the calyptra c ; B Bl plant g- with the nearly ripe sporogo- 
nium, i- its seta, y the theca, c the calyptra ; C longitudinal sec- 
tion of the theca bisecting it symmetrically ; d operculum, 
a annulus, / peristome, c c' columella, h air-cavity, s the pri- 
mary mother-cells of the spores. 
FIG. 267.— Mouth of the theca of Fontinalis 
mitipyretica ; ap outer peristome, i inner peri- 
stome. After Schimper (X 50). 
