BRYOPHYTA 



167 



divisions, resulting in the formation of about four superimposed cells 

 (Fig. 1345-Z)). In each of these vertical walls appear at right angles to 

 each other and later, by the formation of periclinal walls in the upper 

 part of the antheridium, an outer layer of sterile cells is cut off from a cen- 

 tral group of spermatogenous cells (Fig. 134£'~//). The lower portion of 



Fig. 134. Early stages in the development of the antheridium of Marchantia polymorpha, 

 X750. A, division of initial into an inner and outer cell; B, C, D, formation of a filament 

 of four cells from the outer cell; E and F, appearance of vertical walls; G, appearance of 

 periclinal walls; H, later stage, showing sterile jacket surrounding spermatogenous cells, 

 with stalk below. 



the antheridium forms the stalk. By continued division, the spermatog- 

 enous cells give rise to many small, cubical, sperm mother cells, each of 

 which produces two biciliate sperms (Fig. 132B, C). 



The archegonium also arises from a single superficial initial that 

 becomes papillate and divides transversely (Fig. ISoA). Three vertical 

 walls now appear in the outer segment, these being arranged in such a 

 way that a middle cell and three peripheral cells are formed (Fig. 1355, H). 

 The middle cell is the primary axial cell, the peripheral ones the primary 

 wall cells. The primary axial cell, by a transverse division, gives rise to a 

 cover cell and a central cell (Fig. 135C). The archegonium now grows in 



