MOSSES AND LIVERWORTS 111 



note that in its earlier stages it is much simpler than 

 the mature gametophyte, but closely resembles the fully 

 developed thallus of certain Hepaticse whose sporo- 

 phyte is much more highly developed than that of 

 Riccia. 



In all the other liverworts the sporophyte shows a 

 certain amount of vegetative tissue, only a portion being 

 devoted to the formation of spores. The first step in 

 this separation of sporogenous and sterile tissue is the 

 division of the fertilized egg into two cells by a trans- 

 verse wall, the upper part developing into the spore- 

 bearing portion or "capsule," the lower giving rise to 

 an organ of absorption, the "foot" (Fig. 28, C,/), and 

 usually an intermediate region, which forms a stalk or 

 pedicel which elongates at maturity, and causes the 

 sporgphyte to rupture the archegonium-venter, and thus 

 facilitates the scattering of the spores. In most of the 

 Hepaticse the vegetative tissue develops but little chloro- 

 phyll, and the growth of the sporophyte is mainly at the 

 expense of the gametophyte, from which, by means of the 

 foot, it absorbs nourishment very much as a parasitic 

 fungus does from its host. In all of the Hepaticse, except 

 Eiccia and one or two closely related genera, only a 

 part of the sporogenous tissue or archesporium pro- 

 duces perfect spores. The others either remain unde- 

 veloped and serve to nourish the growing spores 

 produced from the other cells, or more commonly they 

 remain undivided and form peculiar cells known as 

 " elaters." These elongate and develop upon the inner 

 face of the cell-wall thickened spiral bands which, when 

 fully developed, are strongly hygroscopic, and by their 

 movements, induced by changes in moisture after the 



