320 Journal of Agricultural Research voi. xix. no. 7 



6 inches high, on June 25, 1919. One scion died immediately, and the 

 hill remained entirely healthy. In the other cases branches from the 

 grafted stalks showed mosaic dwarfing with wrinkling and streak necrosis 

 and some slight mottling in the leaves, while the nongrafted ones re- 

 mained healthy. 



TRANSMISSION WITH PLANT JUICE 



STOCKS TREATED IN 1918 



Although several methods of artificial inoculation performed in 191 8 

 apparently had no effect/ the high percentages of mosaic shown by some 

 of the 191 9 progeny of the treated plants indicate that certain methods 

 were effective. Of 76 plants, progeny of control plants treated with 

 water, 24 per cent were diseased, probably because of aphid transmission 

 in 1 91 8; and of 463 plants, progeny of inoculated plants, 38 per cent 

 were diseased, most of them probably because of aphid transmission. 

 Of one lot of 53 hills, 77 per cent were mosaic. Those developed from 

 progeny of plants which in 191 8 were inoculated by means of capillary 

 glass tubes inserted into the petioles immediately after these capillary 

 tubes were taken from a similar position on diseased vines. All of 

 another lot of 28 hills were mosaic. These were progeny of plants whose 

 stems were split and partly immersed for several days in the juice ex- 

 pressed by crushing the tubers of mosaic plants. These two methods 

 may be regarded as promising effective transmission if used in more 

 extensive trials. 



STOCKS TREATED IN 1919 



In view of the fact that mosaic of potato was transmitted by trans- 

 ferring juice from diseased plants to the rubbed and crushed leaves of 

 healthy plants first under greenhouse conditions,^ it was considered 

 advisable to confirm these results with a larger number of plants and under 

 field conditions. Consequently, during the season of 191 9 a series of 

 similar inoculation experiments was conducted in field experimental 

 plots, both in the open and under insect cages. 



INOCULATIONS WITHIN THE SAME VARIETY IN THE OPEN 



The first inoculation was made when the plants had reached a height of 

 from 3 to 8 inches. The juice was expressed from the vines in a grinder 

 and was separated at once from the pulp by straining through cheese- 

 cloth. At each treatment the undiluted juice was applied to the leaves 

 after they had been bruised with the fingers. At each inoculation the 

 controls were treated with juice from healthy vines before the plants to 

 be treated with juice from mosaic vines were operated upon. One set of 



1 ScHULTz, E. S., FoLSOM, Donald, Hildebrandt, F. M., and Hawkins, Lon A. op. cit. 



