Sexual reproduction 



393 



second division occurs. The new transverse wall cuts off the swollen oogonium 

 from the lower part of the primary oogonium-cell, which becomes a second or 

 upper supporting cell (fig. 247 Bs). Each oogonium has thus two supporting 

 cells, of which the lower corresponds to the supporting cell in (Edogonium. 

 No further division can take place in either of these cells. 



The protoplast of each oogonium becomes rounded off to form a single 

 oosphere or egg-cell, the chloroplast disintegrating and the egg-cell assuming 

 an intensely green colour except at the receptive spot. 



-os 



Fig. 247. A and B, development of the oogonium in Bulbochsete setigera (Both) Ag., x262; 

 pr, primary oogonium-cell ; s and s', upper and lower supporting cells; o, oogonium. C E, 

 formation and escape of the antherozoids in (Edogonium Landsboroughi (Hass.) Wittr., x 262. 

 F and G, (E. Eoscii (L. Cl.) Wittr. ; F, upper part of oogonium with oosphere (os) showing 

 receptive spot and exudation of mucilage from opening of oogonium ; also division of upper 

 cell prior to formation of another oogonium (n, nucleus of future oogonium ; n', nucleus 

 of future supporting cell), x 720; G, oogonium with oospore (oo), but with the male ( 3 ) and 

 female ( ? ) nuclei not yet fused ; aw, a superfluous antherozoid which has entered the 

 oogonium, x 300. (AE, after Hirn; F and G, after Klebahn.) 



There are t'hree distinct sections of the genus (Edogonium characterized 

 by the place of development of the antheridia. In the first type the 

 antheridia arise in the same filament as the oogonia and the plants are 

 monoecious (fig. 248). The other two types are dioecious. In one the 

 antheridia are developed in male filaments similar in character and but little 

 inferior in size to the female filaments. Species in which this occurs are 

 dioecious macrandrous (fig. 249). In the remaining type the male plants are 

 very small and are attached to the female filaments in the vicinity of the 

 oogonia. Such species are said to be dioecious nannandrous (fig. 250). 



