I I 2 
Cavers .— On the Structure and 
Structure and Dehiscence of the Capsule-Wall. 
The wall of the capsule remains one cell thick, except at the apex, 
where there is a small but well-marked cap projecting into the cavity 
of the capsule and consisting of several layers of cells (PL VII, Fig. 48). 
This cap appears to be derived from the uppermost portion of the 
archesporium. The cells of the capsule-wall are at first uniformly thin- 
walled, but thickenings appear later in the form of ring-fibres. At the 
summit of the capsule the cells are much shorter than in the lower portion, 
being cubical in form, whereas lower down the cells are elongated. The 
differentiation of the fibres begins in the upper part of the capsule, and 
we therefore find a gradual transition in passing upwards from the base, 
where the fibres are thinnest and about six occur in each cell, to the apex, 
where each cell contains a single broad ring, which is often so thick 
as to almost divide the cavity of the cell in two (PL VII, Figs. 49-51). 
Besides the ordinary free elaters which are mingled with the spores 
we find a few which are attached at one end to the lowest layer of the 
apical cap, and others which arise from the bottom of the capsule (PL VII, 
Fig. 48). These fixed elaters are shorter and thicker than the ordinary 
free elaters*, and are sometimes, especially at the apex of the capsule, 
intermediate in structure between the free elaters and the cells of the 
capsule-wall, bearing ring-fibres in addition to spirally coiled ones. 
It is easy to isolate a single ripe capsule and to observe the manner 
in which it opens. Dehiscence takes place on drying, and may be hastened 
by gently warming the capsule. A line of cleavage runs round the upper 
portion of the capsule just outside the apical cap. The fissure thus formed 
is irregular and wavy, but it corresponds on the whole with the junction 
between the apical cap and the rest of the capsule-wall. Longitudinal 
splitting then takes place along several (usually from four to six) lines, 
which extend about half-way down the capsule, dividing the wall into 
the same number of valves. The apical cap remains intact, either 
becoming loosened all round and falling off, or remaining attached to 
one of the valves. As the longitudinal fissures extend towards the base 
of the capsule the tips of the valves become rolled backwards, thus 
exposing the mass of spores and elaters. The latter show hygroscopic 
movements, twisting about as they become dry, and thus helping to 
loosen the spores, which may then be either blown by the wind or washed 
away by rain. 
After the archegonium has been fertilized its neck withers, but the 
venter grows actively and closely invests the sporogonium, forming the 
calyptra. Fertilization is immediately followed by the appearance of 
tangential walls in the cells of the venter (Fig. 32, I); the calyptra 
ultimately becomes five or six cells thick, and remains intact until the 
