ON POTATO " LEAF BLOTCH " AND " LEAF CURL." 619 



borne by plants with, diseased foliage in 1909. Several varieties 

 of potato were growing in the neighbourhood of the diseased 

 'Presidents,' but these, without exception, did not take the disease. 



In the third case, a very large field in the neighbourhood of 

 Dunbar had been planted with seed obtained from the Continent in 

 1910. I noticed stunted plants with the characteristic blotched appear- 

 ance of the foliage scattered about here and there among the healthy 

 ones. Some of the diseased plants were dug up, and it was found in 

 every instance that the tubers borne by them were few in number and 

 of negligible size. Nevertheless, the yield from the field in question 

 was exceptionally heavy. This may be accounted for by the fact that 

 the diseased plants were comparatively few in number, and the feeble 

 development of a plant here and there may have corresponded to a kind 

 of ** weeding out " which proved on the whole advantageous to the 

 development of the crop. The disease did not appear on other varieties 

 of potato grown in the same and neighbouring fields. The important 

 points to be remembered are: — 



1. The disease appeared in the crop raised from seed potatos of 

 the ' President ' variety purchased from the Continent on at least three 

 separate occasions (1908, 1909, 1910). 



2. The disease appeared in 1910, among potatos originating from 

 those imported in previous years. 



3. When tubers of large size (from healthy plants) were saved for 

 planting, the proportion of diseased plants obtained in 1910 was even 

 greater than it was in 1909 ; when tubers of small size (from unhealthy 

 plants) were used, practically no crop was obtained in the following 

 year. 



4. Two lots of ' Presidents ' were grown side by side under similar 

 conditions; of these, the one was entirely diseased and the other 

 quite free from disease. 



5. The yield from a field of * Presidents ' grown in one of the 

 finest potato-growing districts of Britain was exceptionally large, 

 although diseased plants which bore tubers of negligible size were 

 scattered among the healthy ones. 



6. The disease did not appear among a large number of other 

 varieties of potato grown on the same field or farm. 



It is difficult to avoid coming to the conclusion that leaf-blotch 

 disease has reached Scotland on at least three separate occasions from 

 the Continent with the * President ' variety of potato, and that there 

 is a marked tendency for the disease to spread in Britain. The fact 

 that, in spite of the presence of diseased plants, large crops of the 

 * President ' have been obtained in some instances may not prove a 

 fortunate circumstance, and it is possible that several additional cases 

 may be reported in 1911. 



It is of course impossible to describe the early symptoms of the 

 disease, since the plants were not seen until towards the end of 

 September and had already formed seed. At this time the unhealthy 



