PLATE 26 



A. — Healthy scion grafted upon diseased stock. Yotmger leaves on scion show 

 typical mottling. Greenhouse, Washington, D. C, 1916. 



B. — An illustration of a method used for introducing aphids. This method resulted 

 in 89 per cent of infection before the plants matiu'ed. In practice the insect cage 

 was left in place while the aphid-bearing leaves on the stick were introduced. Green- 

 house, Orono, Me., April, 19 19. 



