2 75 ' 
Cytology of Pythium ultimum , n. sp . 
was required. Accordingly chunks of potato, carrot, and 
turnip, paste made of starch, flour, pea-meal, and various other 
materials, were sterilized in suitable glass pots and inoculated 
with the relatively pure material obtained from the rhubarb 
leaf cultures. On the second day after inoculation there was 
a growth of pure white aerial mycelium on potato, carrot, and 
turnip a centimetre in height, which on the following day had 
increased to almost an inch. The mycelium indeed quickly 
filled the whole pot. It was obvious that a very simple way 
of obtaining a pure culture had been found. It was only 
necessary to sterilize potatoes and inoculate them with a 
trace of the aerial mycelium. This was done, and the pure 
culture thus obtained provided all the material upon which 
the more important results were worked out. 
Such pure cultures can be obtained, no doubt, with ease in 
many species of Pythium , and it is to be hoped that in the 
future the method described will be largely utilized. 
It is perhaps of interest to add that the attempt to culti- 
vate the Fungus on different kinds of paste yielded negative 
results. 
Observations made on Living Material. 
As already indicated, this species of Pythium has been 
studied in three distinct types of cultures : — (i) Moist-chamber 
cultures, the nutrient material being generally the legs of 
house-flies ; (2) Petri-dish cultures, the nutrient material 
being generally dead flies or bits of cabbage leaves ; and 
(3) Glass pot cultures, the nutrient material being boiled 
potato. 
The glass pots were cylindrical, 4 cm. high, 6 cm. in 
diameter, and of a capacity of about 100 c. cm. In the first 
two types the mycelium develops, with rare exceptions, 
entirely under water and so is aquatic ; in the third the 
mycelium grows out into the air, and so is aerial. In all 
cases certain branches of the mycelium penetrate the nutrient 
substratum, and thus are intramatrical, but the greater portion 
of the mycelium is extramatrical. The intramatrical parts do 
