214 
Hor tog,— Recent Researches 
only slowly roll a little apart on the deliquescence of the 
cell-wall, has nothing to do with the case at all ; and I cannot 
conceive why he refers to it in this connection. 
Rothert denies that in ill-aerated cultures Diciyuchus - forms 
occur ow 7 ing to the zoospores failing to escape. I thought the 
fact notorious, and did not adduce details. Here, however, is 
a crucial case. The cover of a culture was luted to an air-tight 
cell of wood-pulp saturated with paraffin, fixed to the slide 
while warm. The first two zoosporangia to open discharged 
all their zoospores ; the third discharged half, and one remained 
sticking in the passage; many more opened, but all their 
zoospores encysted in the sporange, constituting the Dictyu - 
chits- form. The inference is obvious that they escape to get 
into purer conditions than inside the sporange ; but that I 
pushed this evidence somewhat far in ascribing the stimulus 
to free oxygen is rendered probable by some experiments 
Rothert publishes as conclusive ; they are, however, very im- 
perfect. I shall now discuss these. 
I. Water is boiled in a test-tube and quickly cooled to 
24 0 C. by pouring cold water on the outside ; a square paper- 
cell is put on the slide, filled with the boiled water, and 
covered with a well-fitting cover, so that the water, very poor 
in air, was almost completely shut off from the atmosphere ; 
and we have reason to assume that during the observation it 
remained approximately free from air. Before covering, ex- 
cised Saprolegnia - material with sporangia in various stages was 
introduced, and observed. Both development and liberation 
of the spores was normal, though both were much slackened ; 
no spore remained in the sporange though they soon came to 
rest. 
In answer to this we may note four distinct points. (1) 
The air is very imperfectly expelled from water by a single 
boil up. (2) Air is taken up on cooling, and especially in 
placing on the slide. (3) Slide, cover, and especially paper- 
cell, are coated with an air film which they give up to the 
water. (4) This poor solution of air in water is probably in- 
finitely richer than the inside of the sporange with the active 
