100 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 odspore or fecun- 
dated egg (Fig. 36, G). 
It will thus be seen that while the antheridium of Aléugo 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. 
Fic. 36.— Fusion of sexual nuclei and a young odspore 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 odspore with fusion nucleus which seems to be in 
prophase of division. 
e 
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. dlzté and A. portulacee. 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 
Peronosporee, fecundation consists in the union of one nucleus of 
each sex. In A. tragopfogonis, whose mature egg is uninucleate, 
Stevens finds that the oogonium develops in the same manner as in 
A, blitéand A. portulacee, but it is reduced to a uninucleate condition 
by the disorganization of the supernumerary nuclei. 
