Sept. 17, I9I7 Mosaic Disease of Tobacco 627 



introduced upon young tobacco plants on January 18. These plant 

 lice multiplied rapidly and remained upon the plants in great numbers 

 throughout January, February, and March. On April i the plants 

 were fumigated with the fumes of nicotine obtained by burning paper 

 impregnated with nicotine to destroy the plant lice, which had stunted 

 the plants severely. These plants were allowed to grow for several 

 weeks longer and soon regained their normal green color. At the 

 termination of the experiment none had developed the mosaic disease. 

 A series of control plants of the same age, fumigated at intervals with 

 nicotine fumes obtained as mentioned above to exclude plant lice, 

 remained free from the mosaic disease throughout the period of the 

 experiment. 



Other colonies of Myzus persicae infesting mosaic-diseased tobacco 

 plants produced the disease in great numbers of young tobacco seedlings 

 kept in screened cages. 



During the winter of 1915-16 additional experiments were carried 

 out with colonies of Myzus persicae in the greenhouse at Arlington, Va. 

 Colonies of these plant lice which proved to be free from infection, were 

 found, and many individuals were then transferred to the leaves of 

 mosaic-diseased tobacco plants and allowed to multiply freely upon 

 them. Individuals which had been reared upon these plants were 

 then transferred with a fine camel's-hair brush to 13 young, healthy 

 Connecticut Broadleaf tobacco plants. Twelve of these plants became 

 mosaic-diseased within five to six weeks, one plant only remaining 

 healthy. At the same time 15 control plants, which were kept free 

 from plant lice at all times, remained free from the mosaic disease 

 throughout the experiment. 



In another series of experiments large numbers of Myzus persicae 

 were again transferred from mosaic-diseased plants to two fiats of very 

 young tobacco seedlings. At the same time two similar flats were 

 inclosed in screened cages and kept free from plant lice. Throughout 

 the entire experiment the plants in these flats remained free from the 

 mosaic disease. At the same time, however, great numbers of mosaic- 

 diseased plants appeared in both flats which had been infested with 

 plant lice transferred from the mosaic plants. 



These experiments indicate that the green peach aphid may become 

 an active carrier of the infective principle of the mosaic disease of tobacco ; 

 and they also show that these plant lice do not become active carriers 

 of infection until they have been associated with mosaic-diseased plants. 



Numerous experiments were also carried out in the greenhouse with 

 a large, green species of plant louse, Macrosiphum lactucae Kalt., taken 

 from lettuce plants. Colonies of these plant lice were confined upon 

 mosaic-diseased tobacco plants and finally transferred from these plants 

 at different intervals to very young, healthy tobacco plants. They soon 

 established themselves upon the plants and multiplied so rapidly in 



