West : Ox ^Mosses. 



7 



ported on a short leafless pseudopodium. The calyptra is raised by 

 the theca as a pointed cap, the short seta remains buried in the 

 vaginula. The theca opens by four longitudinal slits, which are 

 closed in damp and open in dry weather. 



The PhascacecB are small mosses, their protonema lives until their 

 spores ripen. The theca only opens by the decay of its wall. The 

 internal differentiation of the theca in Ephouerum and Phascum 

 corresponds to that of the BryacecB^ but in Archidinm an intercellular 

 space is formed in the theca, running parallel to its lateral surface, 

 separating the waJl from the inner mass of tissue, as in the true 

 mosses ; but in these latter a layer of cells parallel to this inter- 

 cellular space produces the spore-mother-cells, while in Archidinm it 

 is only a single cell laying in the inner tissue that becomes the 

 primary mother-cell of all the spores. This cell swells and supplants 

 the other cells, until it lies free in the hollow of the theca ; it then 

 divides into four cells, these each dividing into four spores. 



In the Bryaceoe the sporogonium is always stalked, and the seta is 

 generally long and cylindrical. The theca always opens by a lid or 

 operculum, which is either simply and smoothly detached from the 

 lower part of the theca, or an annulus composed of a layer of 

 epidermal cells is thrown off by the swelling of the inner walls, and 

 thus the operculum is separated. Around the margin of the theca is 

 a peristome, except where gymnostomous. The theca is at first a 

 solid homogeneous mass of tissue, then an intercellular space is 

 formed by means of several layers of cells separating from the wall, 

 but the wall remains attached to the top and bottom of the columella. 

 Rows of cells containing chlorophyll stretch from the wall to the 

 inner tissue, while the outer layer of the wall is developed into a 

 cuticularised epidermis. The third or fourth layer of cells of the 

 inner mass of tissue, which is separated from the annular air-cavity 

 by two or three layers of cells forming the spore-sac, produces the 

 mother-cells of the spores. 



The formation of the j^eristome must now be considered. In those 

 mosses not forming a peristome, the parenchyma of the inner face of 

 the operculum is homogeneous and thin-walled, and dries up at the 

 bottom of the lid of the ripe theca, and the operculum is essentially 

 formed of the epidermis, or it is attached to the columella, and forms 

 a thickening at its summit, projecting over the mouth of the theca, 

 or else it forms a diaphragm over the mouth, as in nymenodomum^ 



(To he continved.) 



