Evolution of Plants 



339 



ckceie. The latter arises as the end cell of a cell row, and is at 

 first conical. Gradually the apex of the cone elongates greatly 

 into a narrow neck, while the basal part swells out as an oogonial 

 cavity, that encloses a rounded egg. Rupture of the tip of the 

 neck and subsequent passage of a spermatozoid do\\Ti the neck 



Fig. 12 — Diagrams of probable stages in evolution of archegonium and 

 antheridium from coleochsetoid to sphseroriccioid and ceratopterid types. 

 1 young, 2 maturing oogonium of ColeochcBte, 3-7 stages from last to arche- 

 gonium of primitive Hepaticfe. la maturing antheridium of Coleochcete. 2a- 

 6a transition stages to Hepaticae. a stalk cell, b ventral cells, c wall cells, d 

 neck cells, e neck-canal cells, f ventral canal cell, g egg, h,i maturation of sperma- 

 tozoids. 



effects fertilization. In hypothetically intermediate and ex- 

 tinct examples, peripheral cell segments must have been cut 

 off as in the antheridia, to form a wall layer; while the oosphere, 

 by cutting off accessory cells in line wdth itself, gave rise to a 

 set of conducting and chemotactically secreting cells, that 

 could guide the spermatozoid down the now multicellular 

 neck to the egg (Fig. 12, 4-7). Finally the perfected arche- 

 gonium of the Ricciese and other Hepatica? has become a 

 stable and practically uniform structure throughout the entire 

 series of the Bryophyta. 



