174 LUTHER BURBANK 



tree is dependent on the circulation of fluids with- 

 in its tissues none the less. These fluids are 

 taken in by the roots, and they find their way to 

 the uttermost leaf. So it is conceivable that by 

 proper treatment of the soil about the tree, the 

 tissues of the tree itself might be so altered as to 

 become resistant to the attacks of the bacterial 

 enemies. 



IMMUNITY THROUGH TREATMENT AND 

 BREEDING 



Nor is this idea altogether theoretical. Ex- 

 periments have already been made that look to 

 the checking of the growth of the tree by with- 

 holding fertilizers and water, that the develop- 

 ment of the tender buds and shoots, which are 

 the usual points of attack of the enemy, may be 

 made to take place slowly and thus to present 

 tissue of a less succulent order. 



Such hardening of the wood by withholding 

 water has proved effective in the case of some 

 pear orchards in Colorado, where it appears that 

 the pear does not really need so much water as it 

 ordinarily receives. 



But the effort to give the tree immunity must 

 go even deeper. Induced immunity is valuable, 

 but the ideal condition is that of inherent resist- 

 ance, bred in the tissues. 



