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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