170 Maine Agricultural Experiment Station. 1920. 



plants showed mosaic symptoms, from field infection. Another 

 part of the same lot was grown near to a group of mosaic plants, 

 of the same variety, which were heavily infested with aphids. 

 Of this portion of the lot, 17 per cent were mottled from the 

 beginning, from field infection. In addition 50 per cent of the 

 group developed mosaic symptoms following dispersal of the 

 aphids from the mosaic group, the plants next to the mosaic 

 group all doing so. 



A lot of 30 Green Mountain tubers in storage produced 

 sprouts which became lightly infested with spinach or common 

 green peach aphids (Myzus persicae Sulz.) from a neighboring 

 heavily infested lot of sprouted tubers that had come from a 

 purely mosaic stock and that later produced mosaic plants. Of 

 these 30 tubers, 17 per cent produced plants that were mottled 

 early, from field infection, while in addition 20 per cent showed 

 mottling later, usually in shoots from eyes of the bud end and 

 therefore probably the ones first to become exposed to aphid 

 attack. A much larger part of the same general stock planted in 

 the field was less than 20 per cent mosaic. 



Green Mountain plants also were grown under insect cages 

 in the greenhouse during the winter of 1918-19. In one experi- 

 ment five tubers were split. A half of each produced a check 

 plant which was uncaged and untreated and remained healthy. 

 Of the other five plants, all were caged, two being treated with 

 aphids from healthy potato plants and three with aphids from 

 mosaic potato plants. The transfers of aphids were made at 

 three different times and were followed finally by tobacco fumi- 

 gation to kill the insects in order to save the plants for later 

 observations. The former two plants remained healthy but the 

 three others became diseased. 



In another experiment with the same variety, 12 tubers 

 produced 53 plants which showed no evidence of mosaic when 

 small. Twenty-one of these, healthy plants, selected so as to 

 represent each of the original 12 tubers, were kept as untreated 

 controls and remained healthy. About half of these were caged 

 until almost full-grown. Eighteen others likewise representing 

 ■each of the tubers were fed upon by aphids from mosaic potato 

 plants. The insects were introduced upon diseased leaves which 

 were laid upon the caged healthy plant when it was young, 

 from 3 to 13 inches tall. The aphids were on the average about 



