July 1. 1920 Transmission of Mosaic Disease of Irish Potatoes 337 



(5) It appears impossible either for infected plants to recover or, 

 so long as diseased stock is not far off and insect carriers exist, to 

 assure the maintenance of health of susceptible varieties by roguing 

 plots or by selecting hills, tubers, or seed pieces. 



(6) Isolation of plants by means of insect cages, as well as elimination 

 of insects in the greenhouse, have maintained stocks disease-free, indi- 

 cating that control of aphids and possibly of some other kinds of insects 

 as well, is the most important means of checking the spread of potato 

 mosaic among susceptible varieties. 



