542 Trow . — -On Fertilization in the Saprolegnieae. 
based on such isolated observations. Statistically considered they were so 
rare as to be without significance. The change from oosphere to oospore, 
even in apandrous forms such as Davis worked with, is easily recognizable 
and should have been specially noted. 
It was, no doubt, a mistake on my part to present the results concern- 
ing fertilization in the two species S. dioica and 5 . mixta , side by side, as 
the additional complexity made it difficult for the reader to realize the 
exact state of affairs without careful study. I ventured, moreover, to 
suggest that the binucleate oospores observed by Humphrey (’ 92 ) in Achlya 
americana , and mistaken by him for oospheres, furnished sufficient 
evidence for the view that another species of Saprolegnieae was also 
functionally sexual. 
There was good ground for this suggestion in the case of Humphrey’s 
work, for he had examined sections and preparations somewhat similar to 
my own. The endeavour, however, to explain Hartog’s (’ 89 , ’ 91 ) results 
on the same lines may have been somewhat rash and certainly gave birth 
to a discussion of a controversial character. The interpretation given of 
Hartog’s observations, however, turns out, so far as it has been tested by 
new observations, to have been justified. 
The view, thus promulgated, that certain species of Saprolegnieae were 
functionally sexual and that the antheridia and fertilization-tubes were not 
degenerate organs, being obviously incapable of assimilation to that pro- 
posed by Hartog, was at once attacked by him. He, however, had no new 
observations to bring forward in support of his contentions, and as it was 
obviously impossible to make any real progress in a controversy of this 
kind, in the absence of fresh evidence, I resolved to continue my work and 
investigate the genus Achlya for myself. It seemed to me at that time, 
and the progress of research has only served to strengthen the conviction, 
that the normal occurrence of two nuclei in the young oospores was good 
presumptive evidence for the occurrence of fertilization. The real value of 
such evidence depends entirely on the previous demonstration, in my own 
preparations, of the uninucleate character of the oospheres. 
In the year 1897 Miss Dawson collected and cultivated a species of 
Achlya , which, on examination, turned out to be a variety of Achlya 
americana. This form was examined by me in great detail in the years 
1897-8, with the result that I (’ 99 ) was able to prove that in this species 
(1) the oospheres are invariably uninucleate, {%) the young oospores are 
binucleate (in one case out of hundreds three nuclei were observed), and 
(3) the old oospores are invariably uninucleate. It cannot be too strongly 
insisted upon that these observations, in the case of this species of Achlya , 
are relatively simple ones, sufficiently so indeed as to form no more than 
moderately difficult exercises for advanced students. The real difficulties 
raised by the investigation of the cytological problems of the Saprolegnieae 
