632 Trow . — The' K ary 0 logy of Saprolegnia . 
seen in the oogonia and antheridia. Hartog, curiously enough, 
has partly verified and accepted these observations. The 
affinity between Peronospora and Saprolegnia is sufficiently 
close to justify us in viewing with extreme suspicion any such 
differences in the karyology as would involve nuclear divisions 
in the one genus and nuclear fusions in the other. 
Although I am not prepared to accept Wager’s results in 
detail, and, for a reason which will appear later, am much 
inclined to give them another interpretation, one must admit 
that the observations show inherent evidence of being 
thoroughly trustworthy : in particular the evidence as to 
nuclear division appears to me to be very strong. I have 
little doubt indeed that Wager’s figures, together with my own, 
furnish considerable evidence for the occurrence of reducing 
divisions in Peronospora also. 
The researches on reducing divisions carried out by Overton 
(’93), Strasburger (’94), and others, make it at any rate not 
improbable that such divisions should take place in the 
Saprolegnieae and Peronosporeae. 
In addition to this positive evidence in favour of the 
occurrence of divisions in the oogonia, it may be useful to 
bring forward what evidence exists as to the improbability 
of nuclear fusions taking place. 
Oltmanns (’95) has shown that in the oogonia of Vaucheria , 
where nuclear fusions were supposed to take place, no such 
phenomenon occurs. A number of nuclei pass into the oosphere, 
but before the basal wall is formed they all pass out again 
with the exception of one, which becomes the nucleus of the 
oosphere, and later unites with the sperm-nucleus to form the 
nucleus of the zygote. I may add that it has been my good 
fortune to have seen some of the sections upon which Prof. 
Oltmann’s conclusions were based. 
So far as I have been able to ascertain, there is no thoroughly 
reliable evidence for the occurrence of the fusion of nuclei 
in the Thallophytes, except in connexion with the sexual 
process. 
It must, moreover, not be forgotten that Dangeard came to 
