Ill 



THE JUNGERMANNIALES 



77 



taking place about the same time as the first division in the 

 archegonial cell (Fig. 31, B). The divisions in the latter are 

 the same as in Riccia, and the general structure of the arche- 

 gonium offers no noteworthy peculiarities. The number of 

 neck canal cells is small, probably never exceeding four, and in 

 this respect recalls again Riccia. The central cell is relatively 

 large, and the ventral canal cell often nearly as large as the 

 Qgg. As the archegonium develops, its growth is stronger on 

 the posterior side, and it thus curves forward. At first the 

 young archegonium projects free above the surface, but pres- 



FiG. 31. — Sphcrrocarpus sp. (?). Development of the archegonium. A-C, Longi- 

 tudinal sections, X6oo; D, X300. 



ently an envelope is formed about it exactly as in Riccia, but 

 arising at a later stage. After this has begun to form, its 

 growth is very rapid, and it soon overtakes the archegonium 

 and grows beyond it, and finally forms a vesicular body, plainly 

 visible to the naked eye, at the bottom of which the arche- 

 gonium lies. The formation of this involucre is quite inde- 

 pendent of the fertilisation of the archegonium, and as these 

 peculiar vesicles cover completely the whole dorsal surface of 

 the plant, they give it a most characteristic appearance. Usu- 

 ally each archegonium has its own envelope, but Leitgeb ( (7), 



