TV 



THE JUNGERMANNIACEJE 



83 



covered that the two-celled gemmae which had been described 

 as formed simply by a separation of the cells of the thallus, 

 were really formed within the cells and expelled from them 

 through an opening, after which they divided into two cells 

 and ultimately developed a young plant, much as an ordinary 

 spore would do. The absence of cilia from these cells, which 

 probably are the last reminiscences of the ciliated gonidia of 



Fig. 33. — Metsgeriapubescens<^a.Ad..). A, Surface view of the thallus in process of division, x8o; B, 

 growing point of a branch showing the two-sided apical cell (x) and the ventral hairs {h), X 240 ; 

 C, the growing point in process of division, x, x', the apical cells of the two branches, X 480. 



the aquatic ancestral forms, is to be accounted for by the 

 terrestrial habit of Amur a. 



The branching is dichotomous, and is brought about by 

 the formation of a second apical cell in one of the youngest 

 segments. This apical cell is formed by a curved wall, which 

 strikes the outer wall of the segment (Fig. 33, C). Thus 

 two apical cells arise close together, and as segments are cut 

 off from each, they are forced farther and farther apart, and 



