Diseases of the Potato. 319 



tioii was to Boak the seed in a solution of corrosive sublimate for 

 one and one-half hours. The solution was made by dissolving 2 

 ounces of the poison in 15 gallons of water. Potatoes treated in 

 this manner are practically free from the scab fungus, as the latter 

 is usually destroyed, unless the potatoes used for seed are very 

 badly injured. In such cases it appears that some of the germs of 

 the disease may escape and serve as sources of infection in the field. 

 In order to overcome this defect the use of stronger solutions have 

 been recommended, or the immersion of the tubers during a longer 

 time. Bolley's latest recommendation is to dissolve 10 ounces of 

 corrosive sublimate in 60 gallons of water, and the general tendency 

 among experimenters is to use stronger solutions than the ones first 

 recommended. The period of immersion also varies from one and 

 one-half to three hours. Probably the period of treatment may 

 vary with the amount of scab upon the tubers, and with the depth 

 to which the tissues are diseased. The germinating power of pota- 

 toes is sometimes impaired if they are treated with the strong solu- 

 tions for the long periods recommended. It is advisable, therefore, 

 to get as clean seed as possible, but if the potatoes are scabby, to 

 treat them with solutions whose strength increases with severity of 

 the disease on the tuber, at the same time lengthening the period of 

 immersion. 



It has been my experience that it is fully as important to have 

 clean land as it is to have clean seed. The fungus causing the 

 trouble appeared upon potatoes which were grown from clean seed 

 upon land that had not been used for this crop during five years, 

 although two crops of beets had been grown upon it during this 

 period. How long the disease may persist is not known, but it was 

 sufliciently severe during the comparatively dry season of 189.5 to 

 obscure the results of several experiments designed to show the 

 value of various treatments of Burbank potatoes for the destruction 

 of the scab fungus. The soil selected is a moderately moist gravel 

 loam. 



Another portion of the field had not grown potatoes for eighteen 

 years, and the land proved to be entirely free from the disease. 

 The portion selected for the experiments is a comparatively dry 

 gravel loam in a high state of cultivation. The attempt was here 

 made to lessen the disease by means of copper and brass shavings, 

 these being mixed with the soil in the drills. No beneficial results 

 from the treatment were observed, however, even when enormous 



