Field Observations on Development of Potato Blight 191 
vigorous growth. The position of the plants particularly noted is 
shewn on the accompanying plan (Fig. 1). 
- F>i-o-r / - 
£'*st 
The record of the observations on Plot 1 is as follows :— 
June 25. A plant, subsequently called plant A, shewed three 
separate brownish-black zones on one of the two main stems 
arising from the parent tubers. These discoloured areas extended 
about two inches upwards from one and a half inches above soil 
level and were suspected of being affected by Phytophthora. Care¬ 
ful search in the vicinity, however, failed to reveal any shoot 
bearing spores which might have been the source of infection. 
A portion of one of these discoloured areas was removed for 
microscopic examination, but by the time (July 1) it reached the 
writer in London, bacterial decomposition was so advanced as to 
prevent the certain diagnosis of Phytophthora although spores 
similar to those of blight were found on the surface. It was 
therefore probably affected by blight. 
On the same day two of the lower petioles were seen to be 
partly withered. 
On this date no similar discolouration was seen in any other 
plant in this plot. 
