LUTHER BURBANK 



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 at- 

 tacks of the aphis may thus be produced. 



Unfortunately the seedlings of the Northern 

 Spy do not generally inherit this quality of resist- 

 ance to the aphis, so it is necessary to grow the 

 roots from cuttings. 



Apple twigs do not root very readily, but if 

 cuttings from vigorous Northern Spy branches 

 are placed in the soil and allowed to grow for a 

 year or longer they develop a good root system 

 and the roots may be severed into small pieces, 

 each of which will produce a stock upon which 

 grafts of any variety may be placed. 

 HYBRID APPLES 



I have experimented very extensively, as al- 

 ready noted, with the crossing of different familiar 

 varieties of apple, and have produced several new 

 varieties that have been deemed worthy of intro- 

 duction. 



But my most interesting experiments have had 

 to do with the wider hybridization in which one 

 or another variety of cultivated apple has been 

 crossed with a related species. In endeavoring 

 to introduce new traits I imported in 1890 all of 



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