279 
pots in each series were mulched with a layer of sterile grass to 
keep the soil constantly, damp. So long as the pots remained 
in the greenhouse the floor of the house and the gravel into which 
the drainage water of the pots ran was regularly watered with 
a strong solution of potassium permanganate as a precaution 
against cross infection between the pots. Later, it was found 
difficult to keep the temperature of the house below 25° C., and 
as, in the laboratory, this temperature had been found prejudicial 
to the growth of Oospora, the pots were taken from the house and 
placed in groups of their respective series at one end of the lawn. 
All the plants made good growth and remained healthy throughout 
the season, and we were thus fortunate in having no complicatory 
diseases to consider in the final results. The above experimental 
details have been given thus fully in order to show that the 
conditions of the experiment were as stringent as it was po:sible 
to make them. 
Results of Inoculations. 
The potatoes were lifted in October, when the same precautions 
against accidental or cross infection were observed as on planting. 
Each pot gave an approximate yield of 1} Ibs.—a serviceable 
quantity to deal with. The soil was dry, and the potatoes from 
each pot were placed directly on lifting into a new brown paper 
bag which was at once closed, but which admitted a free supply of 
air. The bags were then stored in an unheated room during the 
winter, with the exception of one bag from each series which was 
opened and the potatoes washed and examined. These are 
described below, and photographs of the crops from Series 1 and 3 
are given in Figs. 1 and 2. 
Series 1. Oospora inoculation. Tubers absolutely clean and 
indistinguishable from those of the Control pot (see Fig. 1). 
Series 2. Corky Scab inoculation. Every tuber infected 
with the typical sori of Corky Scab in all stages. None of these 
bore any resemblance to Skin spot pustules. 
Series 3. Oospora and Corky Scab inoculation. No Skin 
spot pustules were seen, but the potatoes were covered with sori 
of Corky Scab varying in diameter from 0-5 to 10 mms. Most 
of the sori were unbroken and many were as small or smaller than 
Skin spot pustules, but none could have been confused with the 
latter. (See Fig. 2). 
Series 4. Control. Every tuber was perfectly clean and 
free from blemish. ; 
Each group of photographed potatoes was placed in a clean 
bag and stored in the same place as the remaining crops. 
We had been prepared to some extent by Owen’s(’) work for 
the fact that Skin spot was essentially a storage disease, but, 
in spite of this, we must confess that at this stage we had little 
expectation of seeing any spot or blemish appear on the — 
and glossy skins of the Oospora-infected tubers. In April o 
this year, however, all the bags were opened and we were 
