200 MAINE AGRICULTURAL EXPERIMENT STATION. I9I4. 



a tendency to form tuber-like outgrowths in the axils of the 

 leaves and branches, particularly the lower ones. Examination 

 showed that the fungus had attacked the tuber-bearing branches 

 of the stem below ground and cut them off before or soon after 

 the tubers had set. This resulted in stimulating the plant to 

 produce tubers or tuber-like outgrowths close to the surface 

 or above ground. Fig. 68 shows the base of such a plant grown 

 in a lo-inch flower pot. 



Field Studies and Observations; 



The behavior of plants in the greenhouse, even when grown 

 from samples of the' cleanest tubers produced on the field of 

 Irish Cobblers in 1912, furnished a clue to the cause of the diffi- 

 culty that season. Accordingly about two acres of the original 

 field was replanted in 191 3 with seed tubers produced on the 

 same land the year before, in order to provide an opportunity 

 to study conditions with regard to the crop throughout the 

 summer. The seed tubers were treated with formaldehyde for 

 scab the same as had been done in 1912. In fact an effort was 

 made to have conditions as nearly like those of the previous 

 season as possible except that the crop was being planted the 

 second time on the same land. 



Brown lesions of various sizes began to appear on the sprouts 

 below ground soon after they started from the seed-pieces 

 However, the injury did not begin soon enough or was not 

 severe enough to prevent many of the sprouts reaching the sur- 

 face. About the same time Mr. C. A. Day discovered a field of 

 potatoes in the eastern part of Washington County where the 

 same disease occurred. Fig. 63 is a reproduction of a photo- 

 graph of a potato seed-piece found on this field by Mr. Day. 

 This seed-piece had 3 sprouts and when received one was 

 entirely killed and half of it gone, another was practically 

 dead, and a third so badly injured that it would never reach the 

 surface of the ground. 



Early in July on the field at Highmoor Farm, the plants 

 averaged 6 or 8 inches high after having been covered twice in 

 cultivation. As a whole they appeared strong and healthy above 

 ground, but one or two per cent of them extended but slightly 

 or at the outside not over two or three inches above the hills 

 made by the cultivator and horse hoe. Except that they were 



