166 Maine Agricultural Experiment Station. 1920. 



It is clear that these results, secured under different condi- 

 tions and at various times and places, all indicate that such con- 

 tact of plant tissue as is possible in a graft enables the causative 

 agent of potato mosaic to pass from a diseased plant, or plant 

 part, to one that is healthy, resulting in the latter becoming af- 

 fected also. 



JUICE INOCULATIONS. 



While tests of communicability were being carried on by 

 means of grafts, similar tests with the transference of plant 

 juice were also performed. Both tubers and plants were used. 

 Experiments were made in the greenhouse and field, and three 

 varieties of potatoes were employed. 



The juice from the crushed leaves and stems of diseased 

 plants was introduced into a cavity in a half of a split tuber. 

 Sometimes both the treated half and the untreated half, the 

 latter planted as a control, produced mosaic plants. Often both 

 produced healthy plants. Occasionally only one produced a dis- 

 eased plant and always it was the treated half. Hence it ap- 

 peared possible to transmit mosaic by inoculating seed tubers- 

 with the juice of affected plants. 



Several methods were used in 1918 for introducing juice 

 from crushed plants and tubers into the stems and leaves of 

 healthy plants. .While no treated plants developed mottling dur- 

 ing that season, progeny of some of the groups of plants showed 

 a high percentage of disease the following summer. During 

 the latter season the progeny of check plants, treated the same 

 as the inoculated plants but with water used in place of the juice 

 of a diseased plant, were mosaic in 24 per cent of the hills, prob- 

 ably because of natural transmission in the field in 1918. Progeny 

 of plants whose stems were split and partly immersed for sev- 

 eral days in the juice obtained by crushing tubers from mosaic 

 plants, were all mosaic. Of the progeny of plants which in 1918 

 were inoculated by means of capillary glass tubes inserted into 

 the leaf stalks or petioles immediately after these tubes were 

 taken, filled with juice, from a similar position in diseased plants, 

 *jj per cent were mosaic. Other methods consisting of the ap- 

 plication of juice, by means of a brush, upon rubbed, bruised, or 

 slashed leaves, did not prove so effective. 



