Inter-Relationships of the Higher Bryophyta. 39 
nutrition of the developing spores. This suggestion appears to be 
supported by a variety of facts in the morphology of the capsule in 
the lower Bryophytes. In these plants (Sphaerocarpales, Marchan- 
tiales, Jungermanniales) the archesporium is a cell-mass derived 
from the entire endothecium, and in the great majority of cases 
sterilisation is confined to the formation of elaters, the amphithecium 
giving rise to the capsule-wall; but sometimes an imperfect 
columella of sterile tissue is formed (e.g., Pellia, Aneura ) and there 
is some evidence that the endothecium may contribute to the 
formation of a lens-like cap or apical thickening of the capsule-wall 
(e.g., Reboulia and some other Marchantiales). In these lower 
Bryophytes, the elaters serve to nourish the developing spores, and 
after becoming thickened and losing their original contents they 
act as conductors of water and dissolved salts, finally assisting in 
spore dispersal at dehiscence of the capsule. As sterilisation 
became more definitely localised and complete in the central region 
of the capsule tissue, the elaters would become less important for 
the nutrition of the developing spores, and in the higher Bryophytes 
they have disappeared altogether. The absence of elaters in the 
Mosses may be correlated with the provision of dehiscence 
mechanisms which ensure the gradual dispersal of the spores 
through relatively small apertures. In most of the non-operculate 
(cleistocarpous) Bryales, the capsule is sessile or has a very short 
seta, and is shorter than the leaves which surround it, hence when 
the spores are set free by irregular rupture or decay of the capsule- 
wall they do not fall in a mass to the soil, the leaves acting 
functionally like a peristome and forming narrow spaces through 
which the spores may be gradually dispersed by wind or rain; in 
most of these forms the spores are relatively large and few. In 
some cleistocarpous Bryales, however, there is a well-developed 
seta (e.g., Pliascum ) which may attain a considerable length (e.g., 
Voitia), and in these forms the spores are usually much smaller 
than in cleistocarpous species with sessile or almost sessile capsule; 
in Pliascum, etc., the capsule becomes detached from the seta, 
leaving a basal aperture through which the spores escape gradually 
when the capsule falls away, while in Voitia the entire sporogonium 
becomes detached, and the spores apparently escape (after rupture 
or decay of the capsule-wall) through a slit in the relatively large 
and persistent calyptra. A similar condition occurs in Calymperes, 
in which the persistent calyptra opens by several longitudinal slits. 
In all cases, there is a mechanism of some kind for gradual spore 
