320 Agricultural Experiment Station, Ithaca, N. Y. 



quantities of the shavings were used. It was evident that too small 

 an amount of the metals entered in solution to affect the growth of 

 the scab fungus, although the spores of other fungi are unable to 

 germinate in water which has passed through a copper pipe only a 

 few feet in length. 



An attempt to increase the amount of scab was, however, entirely 

 successful. A small handful of air-slaked lime was scattered in the 

 drills where the pieces of potato were planted, and when these 

 potatoes were dug it was found that the number of scabby potatoes 

 was more than twice as great as in the rows which received no treat- 

 ment ; the individual tubers were also more seriously affected. Air- 

 slaked lime, therefore, appears to have a decidedly favorable influ- 

 ence upon the growth of the fungus. 



An alkaline or an acid condition of the soil becomes a serious 

 matter in certain potato growing regions. This question has been 

 very thoroughly studied by the Rhode Island experiment station* 

 and several of the conclusions obtained are here given, 



" Wood ashes (which, like air slaked lime, consists largely of cal- 

 cium carbonate), pure calcium carbonate, calcium acetate and 

 calcium oxalate, promote the scab in a high degree. 



" Calcium chloride injured the potato plants but entirely pre- 

 vented scab, although an abundance of germs was probably 

 introduced. 



" Calcium sulphate (known as land plaster and gypsum) is the 

 only form of lime employed which has not injured the growth of 

 the crops, and which has at the same time failed to promote with 

 certainty the development of the scab. 



" Upon our acid soil, which has been partially neutralized by air- 

 slaked lime, the use of ammonia sulphate has, under otherwise like 

 circumstances, resulted in producing tubers less scabby than where 

 the same amount of nitrogen in form of sodium nitrate was used. 



"Common salt has reduced the percentage of scab. 



" Sodium carbonate acts in the same way as calcium carbonate, 

 though perhaps not in the same degree, and promotes decidedly the 

 development of disease. 



"Barnyard manure, owing to its alkalinity or the production 

 of carbonate from it, has probably in and of itself increased the 

 scab. 



* Wheeler and Tucker. Bull. 33, pp. 58-79. 



