344 M use INE JE. 
sections. In its lowest type (in Rieda) it is a globe, the outer cell-layer forming 
the wall, while all the inner cells become spores. In all other cases the sporo- 
gonium becomes differentiated externally into a stalk, which may be short or 
long and slender, termed the Seta, and which penetrates into the bottom of the 
archegonium and even into the underlying tissue, its base often becoming dilated, 
forming the Fooi, and a Capsule (Urn or Theca) turned towards the neck of the 
archegonium, in which the spores arise. Together with the spores, long cells 
thickened by spiral bands, the Elaiers, are also produced in most Hepaticse. The 
internal differentiation of the spore-capsule is, in addition to this, very varied, and 
attains a very high degree of complexity, especially in the Mosses. 
While the sporogonium is developing, the ventral portion of the archegonium 
also continues to grow ; its cells rapidly increase in number, and it thus becomes 
broader, enclosing the young sporogonium, and, in this condition, is termed the 
Calyptra. Its behaviour supplies distinctive characters for the larger groups. In 
the lowest Hepaticse (Riccia) the sporogonium remains always enclosed in the 
calyptra ; in the higher Hepaticse it protrudes only after the ripening of the spores, 
its seta elongating suddenly, and the capsule protruding from the ruptured calyptra 
for the purpose of disseminating the spores, the calyptra surrounding the base of 
the seta as a cup-like membranous structure. In the typical Mosses, on the 
other hand, the young sporogonium first assumes the form of a greatly elongated 
fusiform body, which, even before the development of the capsule, exerts a strong 
upward pressure upon the calyptra, which becomes ruptured at its base, and 
is raised up by the young sporogonium in various forms ; the seta penetrates 
deep down into the tissue of the stem, by which it is surrounded as a sheath 
( Vaginula). 
The spores of the Muscinese arise in fours ; the mother-cells — which had 
previously been united into a tissue with the surrounding cell-layers, but had 
become isolated even before the formation of the spores — show a rudimentary 
division into two previous to complete division into four. The number of the 
mother-cells and the place where they are produced in the sporogonium depends 
essentially on the internal differentiation of the latter. The ripe spores show a 
thin cuticle (the exospore) provided with small excrescences, which is ruptured on 
germination by the inner layer of the cell-wall (the endospore). Their contents con- 
sist, in addition to colourless protoplasm, of chlorophyll-granules, starch, and oil. 
The Differ entiaiio7i of the Tissues of Muscinese is very various, and more con- 
siderable than in the Algae, but less so than in the Vascular Cryptogams. Fibro- 
vascular bundles are not found ; only in the stem and leaf-veins of the more perfect 
Mosses is an axial bundle of elongated cells differentiated, which may be con- 
sidered as a slight indication of a fibro-vascular system. The Marchantieae, on 
the other hand, show on the upper side of their thalloid stems, and the Mosses on 
their thecse, a distinctly differentiated epidermis, which usually also forms stomata. 
The cell-walls of the Muscinese are generally firm, often thick, tough, and elastic, 
and in this case frequently of a brown, bright red, or violet colour. The tendency 
towards the formation of jelly and mucilage, so general in the Thallophytes, is not 
found in the Muscinese, with the exception of certain processes in the mother-cells 
of the spores. Various forms of thickening are not uncommon, especially in the 
