266 
Wager .— On the Fertilization 
fertilization, but he comes to the conclusion that in C. candidus 
some of the nuclei remain in the periplasm and contribute 
to the formation of the exospore, the others remain in the 
oosphere, and are there probably joined by the nuclei from 
the antheridium 1 . In Plasmopara densa he made the inter¬ 
esting observation that when the protoplasm concentrates 
towards the centre of the oogonium for the purpose of forming 
the oosphere, two small nuclei are visible at the centre quite 
close together; the other nuclei are found in the periplasm. 
He was, however, unable to say whether these two nuclei fuse 
together or not. 
The question of fertilization in the Peronosporeae remained 
at this stage until the appearance of my paper on Cystopus 
candidus in 1896 2 , in which I described in detail the differ¬ 
entiation of the oosphere, and the fertilization and maturation 
of the zygote. Previous to fertilization, all the nuclei, both 
of the antheridium and oogonium, undergo mitosis. One of 
these nuclei becomes separated from the others in the oogonium 
to form the nucleus of the oosphere, and this then fuses with 
a single nucleus from the antheridium, which passes into the 
oosphere through the fertilizing tube, to form the egg or 
zygote nucleus. This nucleus immediately divides, and by 
subsequent divisions thirty-two nuclei are formed, so that the 
ripe zygote is multinucleate. 
These results were confirmed by Berlese 3 on Cystopus 
Portulacae , and he further extended them to various species 
of Peronospora, P. Ficariae , P. Alsinearum , and P. effusa. 
His observations confirm my own in every important and 
essential detail, except as to the condition of the nuclei in 
the actual fusion. In C. candidus I pointed out that the 
fusion takes place in the resting stage of the nuclei. In 
C. Portulacae and Peronospova Ficariae , Berlese’s figures 
indicate the same thing; but in his figures of P. Alsinearum 
1 loc. cit., p. 128. 
2 On the Structure and Reproduction of Cystopus candidus Lev., Ann. of Bot. x, 
1896. 
8 loc. cit. 
