254 Journal of Agricultural Research voi. xvn.No. 6 



youngest leaves. It was noted also that this mottling occurred only in 

 connection with two very similar treatments. In view of these sug- 

 gestive results, a similar experiment with the more promising of the 

 methods employed in November, 191 8, was begun February 22, 191 9, 



In this experiment healthy plants from 17 different tubers of the 

 Green Mountain variety were inoculated according to the methods indi- 

 cated at the foot of Table III. At the time of planting, each of the 17 

 tubers was halved lengthwise, so that for each treated plant an untreated 

 control plant of the same tuber was obtained. The halves of each tuber 

 were designated respectively x and y and with the same number. Each 

 half tuber was planted in an 8-inch pot. 



At the time of the first inoculation, the height of the plants varied 

 from 2 to 6 inches, and the number of shoots to each half tuber varied 

 from two to seven. As shown in Table III, plants from the tuber halves 

 472X, 483X, 473y, 484X, 471 y, and 485y were treated with juices from 

 healthy plants according to the methods indicated and served as control 

 to the plants treated similarly but with juices from mosaic potato vines. 

 The remaining 1 1 plants, from as many tuber halves, were treated with 

 juices from mosaic foliage. All juices were taken from vines of the 

 Green Mountain variety. 



The performance of the treated and untreated plants is noted in Table 

 III. Number 472y represents the untreated plant and 472X the treated 

 plant developed from the same tuber. At this time observations on 

 foliage of the plants treated according to method 3 with juices from 

 mosaic plants indicated that no mottling had developed. This method 

 failed to produce mottling in the November experiment also. How- 

 ever, with method 5 and with method 7 seven different plants had 

 developed new leaves since March 22; and five of them, or 71 per cent, 

 showed distinct mosaic mottling on the younger leaves formed after 

 the time of the last inoculation on March 22 (Pi. 28, A). The first mot- 

 tling on any of these plants was noted on March 25. On examination 

 March 25 and April 3, 191 9, no mosaic mottling was found on either 

 the old or newly formed leaves in any of the controls, treated or 

 untreated (PI. 27, A, B). All the plants in this experiment were free 

 from aphids. 



