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 

 sporophyte 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 

 Riccia 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 



