■1)4 MUSCINEM. 



ovoid embryo, growing at the end turned towards the neck of the archegonium, 

 viz. the apex. Its final form is very different in different sections. In its lowest 

 type (in Riccia) it is a globe, the outer cell-layer forming the wall, while all the 

 inner cells become spores. In all other cases the sporogonium becomes differ- 

 entiated externally into a slender stalk or Seta which penetrates into the bottom 

 of the archegonium and even into the underlying tissue, and a Capsule (Urn or 

 Thecd) turned towards the neck of the archegonium, in which the spores arise. 

 Together with the spores, long cells thickened by spiral bands, the FAaters, 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 Hepaticee. 



While the sporogonium is developing, the ventral portion of the archegonium 

 also continues to grow ; its cells increase rapidly 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 Hepaticae (Riccia) the sporogonium remains always enclosed in the 

 calyptra; in the higher Hepaticae it protrudes only after the ripening of the spores, 

 its stalk 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 detached 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 

 ( Vag inula). 



The spores of the Muscineae arise i7i fours ; the mother-cells — w^hich 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). Its contents consist, 

 in addition to colourless protoplasm, of grains of chlorophyll, starch, and oil. 



The Differentiation of the Tissues of Muscineae is very various, and more con- 

 siderable than in Algae, but less so than in 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 the fibro-vascular system. The Marchantiese, 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 



