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 
commercial orcharding. 
The other eight strains described are probabV 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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