Sept. IS. I9I9 Investigations 07i Mosaic Disease of the Irish Potato 253 



much wrinkling and some mottling on this new growth; 3 other stocks 

 showed wrinkling only; and the rest remained healthy, even in the 

 rather poorly developed new shoots. 



TRANSMISSION BY PLANT JUICES 



Attempts were made to inoculate tubers of the Green Mountain and 

 Bliss Triumph varieties with juice from diseased plants. In these 

 inoculation experiments the method followed was to divide the potato 

 in half longitudinally, make a cavity in one piece, fill this cavity with 

 the juice from the crushed stems and leaves of the diseased plants, and 

 then plant this treated piece. The other half of the potato was planted 

 in a separate pot as a control. In the first experiment, with four Bliss 

 Triumph and four Green Mountain tubers, all the stalks from four of the 

 inoculated portions of these tubers were typical mosaic plants. One of 

 the control plants, corresponding to one of the inoculated portions 

 which developed mosaic, also showed the disease. These experiments 

 were repeated a number of times with larger numbers of tubers, but only 

 occasionally did the inoculation appear to be successful. In all of the 

 transmission experiments it has been difficult to secure seed-tuber lots 

 which were absolutely free from mosaic contamination, so it was to be 

 expected that occasionally both the inoculated and uninoculated parts 

 of the same tuber would produce diseased plants. On the other hand, 

 the uninoculated controls remained healthy in some experiments where 

 the inoculated seed piece produced a mosaic plant, while the converse 

 did not occur. Hence the evidence secured is presumptive that the 

 disease can be transmitted by inoculating seed tubers with juices of 

 affected plants. 



In northern Maine during the season of 191 8, 50 hills of apparently 

 healthy potato plants of the Green Mountain variety were treated with 

 the filtered and unfiltered extracts from diseased tubers and leaves. 

 These juices were applied by means of painting upon rubbed, bruised, 

 or slashed leaves, and by hypodermic injection into the petioles. The 

 plants at the time of this treatment, July 9 and 10, were about 12 inches 

 tall and in actively growing condition. Obser\-ations on July 20 and on 

 August 17 indicated that no treated plants had developed mottling but 

 appeared like the controls, which were treated with water. In order to 

 note whether this treatment of the foliage had any effect upon the tubers, 

 progeny of these hills was reserved for study in 191 9. 



On November 23, 1918, in a preliminary experiment in the green- 

 house at Washington, D. C, juices extracted from potato vines were 

 transferred to foliage of the Bliss Triumph variety. This operation was 

 performed several times in the course of a month, the first inoculation 

 being made when the plants were 3 to 6 inches high. By December 20, 

 1 91 8, fully 30 per cent of the inoculated plants showed mottling on the 



