184 Repokt of the Department of Botany. 



On April 10 a second plant was placed in the inoculation chamber. 

 It was inoculated twice (April 10 and 16) in the same manner as its 

 predecessor and kept constantly wet for 27 days, but it showed no 

 Phytophthora. Neither did the other four plants in the open 

 greenhouse. 



CONCLUSIONS. 



The negative results of these experiments do not prove that 

 Phytophthora infestans does not persist in the soil, but they make 

 such persistence appear highly improbable. With such an abun- 

 dance of rotten potatoes and with moisture conditions so favorable 

 for infection it is surely remarkable that no infection occurred if 

 there was anything in the soil or potatoes capable of producing 

 infection. 



However, so far as the control of blight and rot is concerned it 

 really does not matter much whether the fungus does or does not 

 persist in the soil. In any case, blight and rot can be controlled by 

 proper spraying and, in New York, at least, the necessity of spraying 

 can not be avoided by any method of crop rotation or by planting 

 disease-free seed. Numerous experiments made in this State have 

 shown that although spraying may occasionally prove unprofitable, 

 particularly in dry seasons, it is highly profitable on the average. 4 

 The spraying of late potatoes should never be neglected. 



While the planting of potatoes after potatoes has a tendency to 

 increase trouble with scab, Fusarium wilt and some other diseases, 

 and is often inadvisable for other reasons, there is no risk in the 

 practice so far as late blight and rot are concerned. 



The removal of diseased tubers from the field, as recommended 

 by Massee, we regard as unnecessary. 



4 The experimental evidence on which this statement is based, also, directions for 

 spraying, will be found in Bulletin No. 347 of this Station. 



