283 
Cytology of Pythium ultimum , n. sp. 
conidium , in the second this conidium develops one or more 
germ-tubes. To provide suitable material for sectioning, 
it was necessary that large numbers of oospores should be 
made to germinate together. After many futile attempts, in 
which the effects of variations in temperature and culture 
media were tried, success was achieved as follows 
A mass of oospores was allowed to stand for some days in 
distilled water. These were then placed in running water 
and examined from time to time. Large numbers of oospores 
germinated. Upon examining such oospores it was found 
that (1) the thick inner layer of the wall of the oospore 
dissolved, (2) the fatty globule disappeared together with the 
lateral nucleus, and (3) the protoplasm increased in amount— 
no doubt at the expense of the reserve materials, and became 
more coarsely granular. The oospore in this changed condi- 
tion resembles a conidium so closely that its real character is 
•recognizable only by its position inside the wall of the 
oogonium. In running water no further development takes 
place as a rule, but if such material be transferred to cabbage- 
water the germination is completed by the outgrowth of one 
or more germ-tubes, such as are produced by ordinary 
conidia. 
Once again it is to be noted that under no circumstances is 
there the slightest tendency to the formation of zoospores. 
Whatever the age of the oospores, the nutrient medium in 
which they are placed, or the temperature to which they are 
subjected, tube germination takes place or no germination 
at all. 
However the conditions which regulate the germination of 
the oospores still require further investigation, as the following 
considerations will show. The method outlined above does 
not always succeed. The reasons for the failures have to be 
determined. Further, when the transference of the half- 
germinated oospores to the cabbage-water is made it is found 
that only a very small percentage (5 to 10) succeed in 
developing germ-tubes. The remainder burst, liberate a por- 
tion of their contents under considerable pressure into the 
