IOO 



FECUNDATION ; HETEROGAMETES. 



Fig. 5 (1. c., 1900) it seems that the plasma membrane might be formed 

 at an earlier stage. The sexual nuclei remain close, side by side, for a 

 short time, and then fuse to form the nucleus of the oospore or fecun- 

 dated egg (Fig. 36, G). 



It will thus be seen that while the antheridium of Albugo Candida 

 contains several nuclei, only one, together with a small portion of 

 cytoplasm, passes into the egg. The egg, although differentiated within 

 a multinucleate organ, contains but one nucleus, and fecundation con- 

 sists essentially of the union of one male with one female nucleus. 



Fro. 36. Fusion of sexual nuclei and a young oospore of 

 Albugo (Cystopus] Candida.. (After Wager.) 



F, the conjugating tube within the egg has disappeared, 



sexual nuclei in contact, surrounded by dense mass of 

 cytoplasm; egg provided with plasma membrane; a, 

 vacuole marking position of conjugation-tube, which 

 has disappeared. 



G, young oospore with fusion nucleus which seems to be in 



prophase of division. 



As already mentioned in a preceding paragraph, a remarkable con- 

 trast is described by Stevens as taking place in two other species of 

 Albugo, namely, A. blitiftnA A. portulacea. In the last two species 

 named the differentiated egg-cell is multinucleate, and, since several 

 nuclei enter from the antheridium, fecundation consists in the union 

 of several male with several female nuclei in the same egg. This is 

 the more remarkable, because in all other species of this genus, so far 

 as the author is aware, and in other closely related genera of the 

 Peronosporece, fecundation consists in the union of one nucleus of 

 each sex. In A. tragopogonis, whose mature egg is uninucleate, 

 Stevens finds that the oogonium develops in the same manner as in 

 A. /?V/and A. portulacece, but it is reduced to a uninucleate condition 

 by the disorganization of the supernumerary nuclei. 



