543 
Trow. — On Fertilization in the Saprolegnieae . 
do not arise in connexion with the rigid determination of these relatively 
simple points. What then was the evidence for the existence of fertilization 
in the Saprolegnieae in 1898? 
In the three species most fully investigated by me, and excluding the 
admittedly apogamous S.ferax , the results were definite enough. 
In Achlya americana cambrica a practically invariable succession had 
been proved ; the uninucleate oospheres become binucleate oospores, which 
as they grow older return to the uninucleate condition. This succession, 
especially so far as concerns the number of the nuclei, may be expressed as 
a formula 1, 2, 1. 
In Saprolegnia dioica the same succession had been shown to occur, 
but the fusion of the gameto-nuclei being long delayed and difficult to 
demonstrate, the last stage in the process still required some corroboration. 
The formula of succession was found to be 1, 2, 1 ? 
In Saprolegnia mixta (apparently not the same species as Davis’s 
6\ mixta) it had been shown that (1) the oospheres were uninucleate, 
(2) the young oospores either uninucleate or binucleate, and (3) the old 
oospores invariably uninucleate. The formula of succession was 1, 1 or 2, 1. 
The formula suggests that parthenogenesis and functional sex exist side by 
side in this species. 
In Achlya americana , investigated by Humphrey, it had been shown 
that the young oospores were binucleate, but there was no evidence as to 
the number of nuclei in the real oospheres. The old oospores were found 
to be uninucleate. The formula in this case would be x, 2, 1. The balance 
of probability is in favour of the view that x=i. 
It is worth noting that in another species of Achlya investigated by 
Hartog, according to his reiterated statements (’ 95 , ’ 96 , ’ 99 ) the formula 
would be #, 2, 1 where # is greater than 2. This, if verified, would make 
the process of fertilization in this case of quite exceptional interest. How 
far Hartog’s views are in accord with the actual facts can only be deter- 
mined by further investigation. Davis (’ 03 ) refuses, as we shall see, to 
accept Hartog’s theory as to the reduction in the number of the nuclei 
in the oogonium by a process of wholesale nuclear fusions. My observa- 
tions lead me to conclude that such discrepancies as exist between Hartog’s 
account and those of other botanists must be due either to errors of 
observation or to such differences in the cytology of the Saprolegnieae 
as have been shown to exist in the single genus Albugo (Cystopus). Further 
investigations by unbiased observers must be made before the question 
can now be finally settled. Taking all the evidence into consideration, the 
view propounded by me in 1899 that ‘fertilization is now known to take 
place in four distinct forms of Saprolegnieae, viz. Saprolegnia dioica , 
vS. mixta , Achlya americana , and Achlya americana cambric a’ may be 
regarded as strictly in accordance with the facts in the case of the three- 
