102 MANUAL OF BOTANY 



bridged over by strands of cells. The amphithccinm gives rise 

 generally only to the wall of the capsule, but in one or two 

 families the sporogenous tissue is derived from it. In most 

 cases the latter springs from either the whole or part of the 

 endothecium. In the latter case a central portion of the tissue 

 remains sterile and constitutes the cohimella. 



The spores are derived from a mass of cells which are earl}' 

 marked off by the richness and granularity of their contents. 

 These are known as the arcJiesjwrmm. In most cases in the 

 Hepaticae the whole of the endothecium becomes sporogenous ; 

 in the remainder (Anthocerotaceae) the archesporium is the inner 

 layer of the amphithecium. In the Mosses it is generally the 

 outer layer of the endothecium ; the Sphagnaceae forming an 

 exception, behaving like Anthoceros. In the genus Archidium 

 of the Mosses the sporogenous tissue is found in the endothecium, 

 but is not regularly arranged as in the other groups. 



In the Hepaticae the archesporium consists of cells which are 

 of two kinds, some sporogenous, giving rise to spores, others 

 sterile, generally becoming elongated and narrow, with a peculiar 

 spiral thickening on their walls. These are known as elaters ; 

 tliey help to disperse the spores when the capsule opens, becoming 

 suddenly elongated by virtue of the longitudinal extension of the 

 spiral band. Elaters are absent from one family of the Hepaticae. 

 the Riccieae, where all the archesporial cells are sporogenous. 



The sporogenous tissue of the archesporium consists of a 

 number of cells with granular contents. Sometimes a good deal 

 of cell-division goes on in this area, sometimes not. Eventually 

 what are known as the mother cells of the spores constitute its 

 substance. In each of these four spores are produced by free cell- 

 formation in the way already described. They are situated at 

 points corresponding to the four angles of a tetrahedron, and the 

 groups are often spoken of as tetrads. Before the spores are 

 fully developed the mother cells separate from each other, and 

 later the spores themselves are set free from the latter, each 

 being now a mass of protoplasm, covered by a cell-wall of two 

 coats which the latter has secreted round itself. 



The spores are liberated by the rupture of the capsule or its 

 decay. When rupture takes place it may be irregular, or by 

 splitting into valves, or by the separation of the upper portion in 

 the form of a lid known as the 02}ercului)}. 



The sporogonium thus formed shows a certain morphological 

 differentiation, there being in the segmentation of the zygote an 

 indic£\,tion of the formation of root and shoot, the latter being the 



