226 LUTHER BURBANK 



Because of the general immunity of the pear 

 to the attacks of the woolly aphis, I have made 

 many attempts to find a variety of pear that 

 would serve as stocks on which to graft apples. 

 In a very few cases the grafts have taken well at 

 first, but the final result was a failure, from a 

 commercial standpoint. It is possible that a 

 variety of pear will eventually be found which 

 will be congenial to the various varieties of 

 apples; and, if so, the problem of combating the 

 woolly aphis will have been solved. There are 

 now several varieties of apples partially or 

 wholly resistant to this pest. 



My experiments consisted in growing seed- 

 ling pears to get new varieties on which to graft 

 the apples. This is probably the only way to 

 approach the subject, for attempts have been 

 made with practically all the existing varieties 

 of pears, and in every case the result has been 

 failure. 



Fortunately there is one well-known variety of 

 apple, the Northern Spy, that is aphis-proof. 

 Trees of this variety are never injured by these 

 insects, even when planted beside trees seriously 

 infected. It has been found expedient, therefore, 

 to graft other varieties on roots of the Northern 

 Spy, and an orchard that has practical immunity 

 to the attacks of the aphis may thus be produced. 



