344 MUSCINE^. 



sections. In its lowest type (in Riccid) 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 Foot, 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 Elaters, are also produced in most Hepaticae. 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 Hepaticae 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 Muscineae 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 Differentiation of the Tissues of Muscineae 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 thecae, a distinctly differentiated epidermis, which usually also forms stomata. 

 The cell-walls of the Muscineae 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 Muscineae, with the exception of certain processes in the mother-cells 

 • of the spores. Various forms of thickening are not uncommon, especially in the 



