LUTHER BURBANK 



extremes of temperature of the northern Missis- 

 sippi Valley, and others are in prospect. 



Especial efforts are being made, also, to de- 

 velop varieties that will be immune to the attacks 

 of the insect pest known as the woolly aphis, 

 which does great damage in apple orchards, es- 

 pecially on heavy soils and in moist climates. This 

 pest is relatively harmless to the treetops, but does 

 great damage when it infests the roots of a tree. 



Because of the immunity of the pear to the at- 

 tacks of the woolly aphis, I have made many at- 

 tempts 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 combatting the woolly aphis will have 

 been solved. 



My experiments consisted in growing seedling 

 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 



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