6i 2 Trow. — The Karyology of Saprolegnia. 
certain amount of amoeboid movement, during which small 
portions of non-nucleated protoplasm are extruded from and 
again absorbed by them, the oospheres become perfectly 
spherical and are then furnished with a thin hyaline border. 
In those species in which antheridia are produced, the 
antheridial branches attach themselves to the oogonium after 
it has attained its full size and before the formation of its 
basal wall. The antheridia are then separated off by trans- 
verse walls. The fertilization-tubes begin to grow out as 
soon as the oospheres have been formed. 
It is obvious from the foregoing that it is very easy to 
identify, even in sections, a large number of successive stages 
in the development of the sexual organs — a matter of con- 
siderable importance in a study involving the accurate deter- 
mination of the relative ages of structures which cannot be 
thoroughly examined in the living condition. 
De Bary (’81, ’83), influenced no doubt by the indubitable 
apogamy of the species destitute of antheridia, came to the 
conclusion that the Saprolegnieae as a group were distinctly 
apogamous : this conclusion was based on his inability to trace 
the passage of protoplasm from the fertilization-tube to the 
oosphere. 
Pringsheim (’82, ’83 b\ as is well known, maintained that in 
certain species at least, fertilization took place. 
I do not propose to enter into the merits of this controversy 
or to discuss the results obtained by other botanists [e.g. 
Zopf (’82, ’83)]. I venture to believe that the methods at 
the disposal of these observers were not sufficiently accurate 
to insure trustworthy results. There seems also to be some 
doubt as to the identity of the appearances described by 
Pringsheim and Zopf. In this paper, however, I hope to 
prove conclusively that the genus Saprolegnia contains at 
least two species ( S.dioica and S. mixta) in which fertilization 
either invariably or frequently takes place, and have little 
doubt that two species of Achlya may be added to the 
list. It is well to lay stress upon this at the outset, since 
under the influence of the great name of De Bary, the 
