6 BULLETIN 624, I T . S. DEPARTMENT OF AGRICULTURE. 



the different strains for commercial fruit production; (2) to determine 

 the extent to which undesirable variations have been propagated, as 

 shown by the percentage of such inferior trees in the present bearing 

 groves; and (3) through improved methods of propagation to 

 control the extent to which undesirable variations in the future 

 shall enter into the population of commercial Valencia orange groves. 

 Briefly stated, these investigations have been undertaken for the 

 purpose of discovering practical methods for conserving and stabil- 

 izing the Valencia orange variety. 



PLAN OF THE INVESTIGATIONS. 



The investigations have been carried on by means of individual- 

 tree performance records and observations. 



The term "performance record" is here used to designate the 

 record of the quantity and the commercial quality of the fruits 

 borne by an individual tree during one or more years. 



The term "performance-record plat'' as used in these investiga- 

 tions means a group of trees grown under comparable conditions 

 and selected for the purpose of determining the relative behavior of 

 the trees by means of individual-tree records of production, observa- 

 tions, and descriptive notes. 



The primary conditions considered in the location of the perform- 

 ance-record plats of Valencia oranges in which the investigational 

 work was conducted were (1) full-bearing trees planted on virgin 

 land, so as to eliminate all possible influence of previous soil or 

 cultural conditions; (2) uniform soil where little or no fertilizers of 

 any kind had been applied and where uniform cultural treatments 

 had been practiced from year to year; (3) the absence of any radical 

 pruning or other tree treatment; (4) the absence or effective control 

 of insect enemies and diseases; (5) trees in a normal, healthy condi- 

 tion, showing satisfactory vegetative growth; (6) a knowledge of the 

 character of the stocks and the sources of the buds used in propaga- 

 tion; (7) sufficient elevation to assure natural protection from frost 

 and other unfavorable conditions; and (8) the prospect of the control 

 of the orchard by the same owners for a series of years. 



These conditions, particularly those of soil and culture, are not 

 conducive to large yields, but are favorable to the study of inherent 

 individual-tree variability and behavior. As the object of these inves- 

 tigations is not the measurement of the highest possible yield or the 

 study of the influence of cultural conditions on the production of large 

 crops, but rather the behavior of trees under conditions as nearly 

 natural as it is possible to secure in commercial citrus orchards in 

 California, it was deemed wise in this selection to eliminate so far as 

 practicable all local environmental influences and abnormal condi- 

 tions. 



