6 BULLETIN 624, IT. 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. 
