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W. Watson. 
of the spore-sac depending almost entirely on the gametophyte. 
In the Jungermanniales, till the spores are mature, the capsule is 
enclosed by the calyptra and surrounded by more or less modified 
perichsetial leaves, besides being usually surrounded by a special 
envelope (perianth) which begins as a ring at the base of the 
archegonial group, and keeps pace with the growth of the egg, 
though its production is generally independent of the occurrence of 
fertilisation. In some cases (e.g., CepJmlozia media) the perianth is 
bistratose. In the Marchantiales the sporogonia are sunk in the 
archegonial cavity (e.g., Riccia) or the sporogonia are developed in 
heads (carpocephala) on the summits of bulky stalks belonging to 
the gametophyte, but usually developed after fertilisation, or even 
after the spores have matured. The involucral scales and hairs, the 
perigynium and the ventral position of the capsules are sufficient 
protection from dryness. 
The special protective devices adopted by the sporogonium 
may be classed under the following heads. 
(1) Immevsion of the Capsule amongst the perichsetial leaves, 
the seta being short or absent. This is often found in xerophytic 
mosses, and sometimes the perichsetial leaves are much longer and 
finer-pointed than the vegetative leaves (e.g., Archidium alterni- 
folium, Pleuridium spp., Fig. 1, 3, 4), or they may be ciliated 
(Diphyscimn foliosum, Fig. 1, 5) or convolute ( Acaulou muticnm). 
As examples of British plants may be mentioned Cryphcea hetero- 
walla, Hedwigia ciliata, Blindia ccespiticia, Physcomitrium pyriforme 
(Fig. 1, 8) and many species of Orthotriclnim, Grimmia, Phascum, 
Ephemerum, Andrecea, Neckera, Coscinodon and Weisia. 
(2) The Length of the Seta varies greatly according to the 
species and seems to be more or less independent of the habitat, as 
the greater length tends to ensure increased efficiency in spore- 
dispersal, but many species, which grow in dry situations have a 
form or variety of a damper habitat, and the seta of this is often 
longer than in the type. Tortula muralis is very variable in this 
respect, the var. rupestris of wet rocks, having a longer seta than 
the type, whilst the form of dry calcareous rocks has a shorter one; 
Brachythecium velutinnm, when growing in moist or shady situations 
has longer setae than when in a drier position. 
(3) Curvature of the Seta, so that the capsule is wholly or 
partially sunk amongst the leaves of the gametophyte. When the 
spores are ripe, the seta more or less straightens out and the spores 
fire dispersed, e.g., many species of Grimmia (Fig. 1, 1), Campylopus 
