146 BULLETIN 623, U. S. DEPARTMENT OF AGRICULTURE. 



The Washington strain is the most important and valuable one. 

 The Thomson strain is also of value, and the Golden Nugget, Yellow 

 Washington, and Yellow Thomson strains are of possible value for 

 co mm ercial orcharding. 



The other eight strains described are probably of little commercial 

 value, and their presence in established orchards is one of the principal 

 causes of the low and poor production of many of them. 



The undesirable strains usually have been propagated uninten- 

 tionally by reason of a lack of knowledge of their existence and 

 importance. 



All of the strains described can be isolated through bud selection 

 based on individual-tree performance records. Fruit-bearing bud 

 wood, with representative fruits attached, should be used for propaga- 

 tion purposes. 



Established trees of unproductive and undesirable strains have been 

 top-worked successfully with buds selected from the best trees of the 

 Washington strain. A practical method for locating such trees and 

 a discussion of their treatment in commercial orchards is presented 

 in Farmers' Bulletin 794 of the United States Department of Agri- 

 culture, entitled " Citrus-Fruit Improvement: How to Secure and 

 Use Tree-Performance Records." 



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