38 



MOSSES AND FERNS 



CHAP. 



and probably always, a single apical cell is developed at the 

 apex at a very early stage. Probably this initial <-e\\ is one of 

 the four terminal octant cells resulting from the first divisions. 

 This cell sometimes has but two sets of segments cut off from 

 it at first, alternately right and left, but whether this form is 

 constant in the young plant I cannot now say. 



Fig. g,—Riccia trichocarpa. Later stages of germination. A, from below, X260; 

 B, optical section of A, showing apical cell x, XS20; C, X85; r, rhizoids. Inter- 

 cellular spaces have begun to develop. 



The four lower quadrants also divide, at first only by 

 transverse walls, and these cells lengthening give rise to a 

 cylindrical body composed of four rows of cells, terminated by 

 the more actively dividing group of cells at the summit. The 

 single apical cell is soon replaced by the group of initials found 

 in the full-grown gametophyte, and the method of growth from 



