American Species of Marchantia. 227 



Each group of archegonia is enclosed by an involucre, which 

 consists of a pair of membranous structures often toothed or 

 laciniated on the margin (Figs. 2, M; 4, F, G; 8, K; etc.)- 

 Each archegonium is further protected by a campanulate pseudo- 

 periantli contracted at the mouth to a small opening. It begins 

 its development soon after the archegonium is formed but does 

 not reach full maturity unless fertilization has taken place. The 

 pseudoperianth is very delicate and becomes irregularly torn 

 when the stalk of the sporophyte elongates. 



6. Sporophyte 



The sporophyte, as in all the Marchantiaceae, shows the usual 

 differentiation into foot, stalk and capsule. The foot is flat- 

 tened and forms a low ridge enclosing the base of the stalk. The 

 latter is at first very short, but it elongates sufficiently at maturity 

 to push the capsule through the calyptra and beyond the mouth 

 of the pseudoperianth. The capsule constitutes the principal 

 part of the sporophyte. It is nearly spherical in form and is 

 boimded on the outside by a wall composed of a single layer 

 of cells. These cells throughout the genus have brownish ring- 

 like thickenings in their walls, although the rings are often 

 incomplete. The entire cavity of the capsule is filled with spores 

 and elaters. The spores are much smaller than in most genera 

 of the Marchantiaceae, especially in M. polymorpha and its allies. 

 In some cases a distinct border is present where the spherical 

 face meets the three plane faces, and under these circumstances 

 low and irregular surface lamellae are usually developed. In 

 other cases the spores are destitute of distinct markings and 

 become completely rounded off after the tetrads break up. The 

 elaters are long and slender and of the usual type, showing two 

 distinct spiral bands. At maturity the wall of the capsule splits 

 from the apex to about the middle into an indefinite number of 

 lobes, some of which may become further subdivided. There are 

 apparently no very definite lines of dehiscence, the edges of the 

 splits being irregular and jagged from projecting cells which 

 formerly interlocked. Except for the spores, which differ in size 

 and in the peculiarities of their walls, the sporophyte yields very 

 few differential characters. 



