320 LUTHER BURBANK 



insects. Varieties of grapes are grown which re- 

 sist the attacks of phyloxera, and apples which 

 are resistant to the attacks of aphis are well 

 known. 



Peaches and almonds which are not subject to 

 curl leaf have been developed. 



Plums which are not affected by the brown rot 

 and plum pocket are now on the market, also 

 cherries, pears, walnuts, and perhaps chestnuts, 

 which are resistant to blight. 



Because of the value to be secured from crops 

 which need not be rotated, too much emphasis 

 cannot be placed upon the importance of devel- 

 oping new plants for this purpose which are 

 resistant to the various pests. 



It will almost always be found that in fields 

 badly affected with some disease or insect there 

 are one or more plants which are not affected as 

 seriously as the rest of the crop. By selecting 

 such plants and perpetuating them by seeds or 

 division, a new variety may eventually be pro- 

 duced that is resistant to the particular disease 

 or insect which caused the damage. 



If resistant plants were developed many old 

 field and garden soils which have become worth- 

 less for certain plants could be made to produce 

 profitable crops. Such soils are quite often thor- 

 oughly infested with numerous insects and dis- 



