juiyi, I920 Transmission of Mosaic Disease of Irish Potatoes 323 



Application of Juice from Plants Showing the Bad Stage of Mosaic 



In order to determine whether juice taken from plants badly diseased 

 with mosaic and introduced into healthy plants would induce bad 

 mosaic symptoms in the latter, plants of the Green Mountain, Bliss 

 Triumph, and Irish Cobbler varieties were inoculated in the same manner 

 as those mentioned in Table IV. Three applications at weekly intervals 

 were made upon plants of the same variety as that from which the juices 

 were expressed. The height of the vines at the time of the first inocula- 

 tion varied from 2 to 8 inches. Plants of five Green Mountain hills, three 

 Bliss Triumph hills, and five Irish Cobbler hills were treated. At the 

 same time also two Green Mountain, three Bliss Triumph, and two 

 Irish Cobbler hills were treated with but a single inoculation. 



On July 28, 16 days after the first treatment, the first mosaic mottling 

 was noted upon the inoculated Irish Cobbler vines. By August 1 5 every 

 inoculated plant, regardless of variety, showed distinct mosaic mottling 

 as well as streaking and ruffiingof the leaves as in the bad stage of mosaic; 

 and by August 28 most of the leaves on the lower half of the stems were 

 dead. The plants subjected to but a single inoculation showed symp- 

 toms similar to those given three successive treatments, indicating that a 

 single treatment may be sufficient to induce the disease (PI. 56). 



INOCULATIONS WITHIN THE SAME VARIETY UNDER INSECT CAGES 



Early Repeated Application 



Juice from crushed mosaic plants (not necessarily mottled at the time 

 of the first inoculation but from stock all mosaic in 191 8) was applied 

 to the bruised leaves of two hills in each of three caged tuber units on 

 June 13, 20, and 27, and on July 5. As a control, the third hill in each 

 cage was left untreated; also juice from apparently healthy plants was 

 applied to the bruised leaves of two hills of each of three other caged 

 tuber units on the same dates. In all these cases the plants were from i 

 to 6 inches high at the first treatment. On July 9 the topmost leaves of 

 the treated hills in the former three units began to show mottling, which 

 was slight to medium by July 15. On July 30 mosaic branches in these 

 units were tagged and were found at digging time, August 26, to belong 

 to the treated hills, which had no healthy stalks. The tuber units upon 

 which the juice from healthy plants was used remained green and 

 healthy until digging time, while those died which became mosaic. 



Late Application 



On July 14 two hills in each of two caged tuber units were treated with 

 juice from mosaic plants in the same manner as those described in the 

 two preceding sections. Before August 20 the upper leaves of the 

 treated hills became mottled and streaked. 



