281 
Series 2. Corky Scab inoculation. 
The tubers in all four pots were badly disfigured with the 
sori of Corky Scab varying in diameter from 0-5 to 20 mms. 
The whiteness of the skin between the sori made it an easy matter 
to examine the tubers, but not a single pustule in any way 
resembling Skin spot could be found. 
Series 3. Oospora and Corky Scab inoculation. 
In all four pots a heavy infection of Corky Scab occurred 
similar to that shown in Fig. 2. Some typical discrete Skin 
spot pustules intermixed with the Corky Scab sori were also 
found as follows :— 
No. of tubers No. of tubers per pot showing 
Pot. per pot. typical Skin spot pustules. 
3 17 4 
B, 18 6 
C. 20 8 
D. 28 1 
The pustules were precisely similar in appearance to those of 
Series 1, and, as there, they appeared mainly in the potato eyes. 
Sections of these were made, but no plasmodia were seen and 
in every respect the internal structure was identical with that 
of typical Skin spot 
In addition to ae above, a few pustules were found in this 
series in which a mixed infection appeared to have taken place. 
Two of these pustules were closely examined. At first glance 
they were apparently normal Corky Scab sori 4 mm. in diameter 
on which the layer of spore balls was plainly visible. On closer 
examination, however, one or two blackish spots were seen on 
the surface, and on cutting through the sorus, the tissues were 
found to be darker in colour than is ustial in Corky Scab. Micro- 
scopic examination showed the presence of a heavy layer of spore 
balls on the surface, and in the tissue below some hyphae were 
seen which closely resembled O. pustulans. It is very possible, 
therefore, that a mixed infection of the two parasites had occurred, 
and considering the heavy inoculums given of both fungi, it 
would have-been rather strange if the infection had not coincided 
at some spots. There were, however, no indications of any 
effect of the one organism on the other taking place in these dual 
infection pustules such as was hypothecated before the experiment 
was carried out. . 
Series 4. Control. 
Pot A. Here, unfortunately, a slight but definite con- 
tamination with Corky Scab had occurred, and two of 
. the tubers showed small typical sori of the disease. No 
appearance of Skin spot was seen, however, and the 
remaining tubers were perfectly clean. 
