Trow.— The Karyology of Saprolegnia. 621 
the slides were satisfactorily stained ; towards the close of the 
work, however, I succeeded in obtaining uniform results. 
Simultaneous fixing and staining by picro-nigrosin can 
readily be carried out, and may be recommended for demon- 
stration purposes ; this method does not appear, however, to be 
suitable for detailed critical study. 
Karyology. 
At the commencement of my investigation of the karyology 
of the genus Saprolegnia— the main object of the research — 
I devoted myself to the examination of pure cultures of 
5 . dioica , De Bary — a diclinous species whose histology had 
till then, apparently, never been studied. In the summer 
of 1894 I was able to prove to my own satisfaction, and to 
that of Prof. Oltmanns, that fertilization took place regularly 
and normally in this species. In view of the controversies 
which have so long raged over this point in the Saprolegnieae, 
we both thought it advisable to make a special study of 
a species destitute of antheridia. I soon obtained pure 
cultures of 5 . Thureti , De Bary, which is, for all practical 
purposes, destitute of antheridia. After maintaining the purity 
of this culture under microscopic control for about six genera- 
tions, large quantities were grown, fixed, and preserved in the 
usual way. These were not previously examined microsco- 
pically. I depended entirely upon macroscopic examinations 
with respect to the determination of the condition of the 
cultures, and that of course with a view to avoiding the 
handling of the specimens as much as possible, and thus 
securing better results. The first sections examined revealed 
the presence of oogonia with and without antheridia. Suspect- 
ing that in some inexplicable way the cultures had become 
impure, I re-examined them in the fresh condition, and found 
that the cultures now appeared to be a mixture of 5 . Thureti , 
De Bary, and ,S. mixta , De Bary. These forms are so closely 
allied, that but for the fact that De Bary found the first to 
maintain its characters for eleven years, and the second for five 
