6 1 8 Trow. — The Karyology of Saprolegnia . 
a single spore upon it which had already commenced to 
germinate. The culture was continued in a moist chamber 
and observed day by day until the sporangia characteristic of 
Aphanomyces and the sexual organs characteristic of A. laevis 
were produced in succession. 
It is worth mentioning that I have found hard-boiled white of 
egg, cut up into minute oblong pieces and floated on the surface 
of the water in the jars containing the cultures, to be a very 
good substitute for flies. At the commencement of the 
investigation, most of the cultures were carried on on meal- 
worms ; later on white of egg was tried and used, but finally 
house-flies were found to be, upon the whole, the most satis- 
factory: if kept dry, as Humphrey (’ 92 ) has pointed out, 
they retain their nutritive properties for at least six months. 
The vitality of these cultures is great : they may be 
neglected for six months, and still on adding fresh food- 
material, new growths at once appear. In the winter of 
1894-1895 some of my jars containing cultures of S.dioica , 
which stood near an exposed window, had the water which 
they contained converted into solid masses of ice, but never- 
theless fresh cultures were obtained from them when the ice 
melted. 
The species I have principally examined in pure cultures 
and in the fresh condition have been .S'. dioica , De Bary, 
S. Thureti , De Bary, and Achlya prolifer a (Nees, 1823), De 
Bary. I have carried the study no further than to satisfy 
myself of the correctness of De Bary’s descriptions and to 
learn to discriminate the various stages in the development of 
the sexual organs for use in the detailed study of serial 
sections : such studies of fresh material are easily carried out 
in moist chambers by means of small cultures on the legs of 
flies. I have found that by changing the water the whole 
course of development (excepting naturally the germination 
of the oospores) may in this way be followed on a single 
culture. 
The four species mentioned do not, however, include all 
those which I have been able to identify. Apodya lactea 
