34 



MOSSES AND FERNS 



CHAP. 



The Embryo 



After fertilisation is effected the egg develops at once a 

 cell-membrane and enlarges until it completely fills the cavity 

 of the venter. The first division wall is more or less inclined 

 to the axis of the archegonium, but approaches usually the 

 horizontal. The lower of the two cells thus formed divides 

 first by a wall at right angles to the first formed, but this is 

 followed in the upper half of the embryo by a similar division, 

 so that the embryo is divided into nearly equal quadrants. In 



m. 



Fig. 6. — A, B, Young embryos of R. glajica in longitudinal section, showing the venter of the arche- 

 gonium, X260; C, transverse section of a similar embryo, X260; D, longitudinal section of the 

 archegonium and enclosed embryo of ii. hirta at a later stage, X220; m, the sterile cells of the- 

 sporogonium. 



each of the quadrants a wall meeting both of the others at 

 right angles next appears (Fig. 6, C, III), and the embryo at 

 this stage consists of eight nearly equal cells. The next walls 

 are not exactly alike, but the commonest form is a curved wall 

 (Fig. 6, C) striking two of the others, usually walls II and III, and 

 intersecting the surface of the embryo. This wall divides the 

 octants into two cells, which appear respectively triangular and 

 quadrilateral in section. By the next division the archesporium 

 is separated from the wall of the sporogonium. These walls 



