126 Report of the Botanist of the 



rows in Series III resulting from the first application of arsenic in 

 lime water July 14. (See page 123). 



Although carefully watched for, no trace of late blight, Phytoph- 

 thora infestans, was found in the experiment field until August 24. 

 Up to this time the sprayed rows were no better than the unsprayed 

 except that they showed somewhat less injury from the unknown tip- 

 burn. The plants were looking well. In places they met between 

 the rows but the ground was not entirely covered by them. Imme- 

 diately after its first appearance the blight spread rapidly. It soon 

 became evident that the north (lower) end of the field would suffer 

 most. Not only was the soil here wetter and the air circulation 

 poorer but there was also a small patch of blight-infested early pota- 

 toes not more than twenty feet distant. 



At the north end, the unsprayed rows had lost a large part of 

 their foliage by September i, and what remained was badly spotted. 

 There were also a good many points of infection on the rows sprayed 

 three times (Series II) but the rows sprayed every two weeks 

 (Series I) were almost perfect in foliage. At the south end of the 

 field there was little if any contrast in appearance between the sprayed 

 and unsprayed rows, although the latter were slightly affected. 



On September 3 the unsprayed rows, at the north end, were pro- 

 nounced dead. 



On September 7, at the north end, the 3-sprayed rows were 

 sufficiently attacked to affect their growth slightly and by Sep- 

 tember 14 they were dead. The rows sprayed every two weeks 

 lived until September 21. Thus it appears that, at the north 

 end of the field, three sprayings prolonged the life of the plants 

 II days while 5 sprayings prolonged it 18 days. 



At the south end of the field the 3-sprayed rows outlived the 

 unsprayed by fully three weeks and were finally pronounced 

 dead on October 3 ; while the rows sprayed every two weeks 

 lingered along until October 7. 



