132 Trow. — Observations on the Biology and 
A careful study of Prof. Hartog’s work, the detailed 
criticism of which may be deferred for the present, convinced 
me that it would be necessary to examine a species of Achlya , 
and so acquaint myself at any rate with the two genera 
specially studied by this observer, before attempting to 
explain the discrepancies in our results. The genera Achlya 
and Saprolegnia agree with one another in nearly all their 
morphological features, with the exception of the order of 
formation, and the mode of dehiscence, of the sporangia. 
The genera can scarcely be distinguished, indeed, by reference 
to the mycelium and sexual organs alone. There are 
interesting differences, however, in the cytology of species 
of Saprolegnia , and it was not improbable that these would 
be accentuated in the genus Achlya and serve to explain 
the differences in the results obtained by the different 
observers — Hartog, Humphrey, Dangeard, and myself. 
Other reasons than those furnished by Hartog’s paper, 
and the discrepancies which have just been referred to, urged 
me to undertake a cytological investigation of a species of 
Achlya. Although the matter had escaped criticism, it was 
clearly desirable to follow the germination of the oospores 
and the nuclear divisions in the gametangia in one and the 
same species of Saprolegnieae, and even more so to determine 
accurately the nature of the chromosome-like body in the 
centre of the nucleus. Zimmermann’s view as expressed in 
the following sentence was clearly untenable : — ■ Es diirfte 
aber wohl kaum zweifelhaft sein, dass der von Trow als 
Chromosom gedeutete Korper in Wirklichkeit als Nucleolus 
zu bezeichnen ist.’ It was advisable, moreover, to put my 
surmise as to the meaning of the binucleate and uninucleate 
oospores of Achlya americana to the test of actual observation 
so far as possible. 
Such a task could not be lightly entered upon — it was 
necessary to find a suitable species ; to grow it for generations 
separated from other forms so that certainty might be attained 
as to its systematic position ; to follow its life-history and 
every stage in the course of its development by direct 
