MUSCINEAE. 



143 



and either serve only as nutrient cells to the spore-mother-cells which by degrees 

 consume the food-material stored up in them, as happens in Riella, or develope 

 into fusiform elaters with spiral thickenings, whose function it is to loosen the S{)Ore- 

 masses at the dissemination of the spores. 



The spores of the IMuscineae are formed by fours through division of the mother- 

 cell into four after previous bipartition of the nucleus ; the mother-cells were pre- 

 viously connected with one another and with the surrounding cell-layers into a tissue, 

 but become isolated before the spores are formed. The mature spores have a thin 

 cuticle, the exosporium, beset with small excrescences, which is ruptured in germina- 

 tion by the inner layer of the cell-wall, the endosporium, and contain a colourless 

 protoplasm, chlorophyll-corpuscles, starch and a fatty oil. 



There is less variety in the construction of the tissues in the Muscineae than in 

 the Thallophytes. In the latter the more complex tissues are the result either of the 

 interweaving or concrescence of originally separate elements or of cell-division, but the 

 latter is the only mode found in the Muscineae and in the forms above them. But the 

 anatomical differentiation is still very simple; all the cells of the vegetative body are 

 alike, as in many of the thalloid Jungermannieae, or an assimilating tissue-system is 

 differentiated from a conducting tissue, as in the Marchantiaceae. The small stem of 

 the leafy forms has usually a thickened cortical layer, and in the Mosses often an 

 axile bundle of elongated cells, such as forms the ' midrib ' in many thalloid species. 

 In the most highly developed forms bundles of narrow cells from the nerves of the 

 leaves join on to the bundle in the stem. Peculiar mucilage-passages are found in 

 the thallus of Fegatella, elongated isolated fibre-strands in that of Preissia, both 

 genera of the IMarchantiaceae. 



CLASSIFICATION" OP THE MUSCINEAE. The sexual generation is 

 developed from the spore, after previous formation of a protonema which in many of 

 the Hepadcae is not sharply distinguished from the plant formed upon it ; it is longer 

 lived than the asexual generation and is the self-supporting vegetative body in these 

 plants, and is either a flat thallus with dichotomous ramification, or a filiform stem 

 with two to four rows of leaves. Vascular bundles are absent. The archegonia and 

 antheridia, except in the simplest thalloid forms, are structures of cellular tissue, 

 stalked and usually free, though sometimes becoming immersed in the thallus by 

 subsequent luxuriant growth of the adjacent tissue. The central cell of the arche- 

 gonium produces the oosphere by rejuvenescence of its protoplasm into a primordial 

 cell. The spermatozoids are threads coiled spirally with two cilia at the anterior 

 pointed extremity. The second or asexual generation, the sporogonium, is formed 

 from the oosphere within the venter of the archegonium ; the venter grows rapidly as 

 the oosphere developes and is thus transformed into the calyptra. The sporogonium 

 is not self-supporting but dei-ives its noui-ishment from the sexual generation, and has the 

 appearance of being an appendage of it ; it is usually a stalked capsule, in which, in 

 every genus except Archidhmi, an archesporium is differentiated, from which the 

 spore-mother-cells are formed either directly or after further divisions ; the spores are 

 formed by division of the mother-cells into four parts. 



I. Hepaticae or Liverworts. The first or sexual generation is formed from 

 the spore with the intervention of a protonema which is usually small antl unimportant; 

 it is either a flat dichotomously-branched thallus, or a filiform stem with two to three 



