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



it is possible that some of them may be found to be more important 

 than they are thought to be at the present time. 



The great amount of variability within the Washington Navel 

 orange variety has been thought by some to be coordinate with the 

 abnormal conditions of its flowers and fruits. Subsequent investiga- 

 tions of varieties of citrus fruits other than the Washington Navel 

 orange have proved that all citrus varieties thus far studied are subject 

 to the variability arising from bud variations in about the same 

 degree as is the navel orange. 



Naturally many differences in fruits and trees are the direct result 

 of the effect of environmental conditions. These seasonal fluctua- 

 tions probably are of no importance from the standpoint of heredity 

 and the stabilization of the variety, as apparently they are not trans- 

 mitted by budding. Performance records showing these differences 

 are, however, important from the standpoint of an investigation of 

 cultural practices, in that they offer direct and valuable evidences 

 of the effect of cultural treatment or other environmental factors 

 upon tree behavior. These investigations have shown clearly that 

 in cultural experiments, such as those in fertilization, irrigation, or 

 other soil treatments, and in pruning or other methods of tree care, 

 the effects of these treatments can well be measured by means of 

 individual-tree records both before and during the experimental 

 period. Individual-tree performance records afford exact data from 

 which to draw conclusions as to the results of such experimental 

 work. 



The extent of the occurrence of diverse strains of the Washington 

 Navel variety in established bearing orchards was found in subse- 

 quent investigations to be much greater than was apparent in the 

 preliminary study of this subject. The lowest percentage of off- 

 type trees, i. e., marked variations from the best or Washington 

 strain, found in commercial orchards, has been about 10 per cent, 

 and the highest about 75 per cent, of the total number of trees in the 

 orchard. These figures do not refer to the many variations in fruits 

 observed in the trees of the Washington or best strain, many of which 

 are probably different enough from the Washington fruits to be 

 classed as true strains, but owing to our incomplete knowledge of 

 the subject they are of necessity for the present included with the 

 Washington strain fruits. 



The name Washington has been adopted for the typical strain of the 

 variety because it represents that type of tree and fruits which was 

 originally intended for propagation by the growers. It is the strain 

 upon which has been founded the reputation of the variety and 

 which under present conditions is the most desirable from commer- 

 cial and other standpoints for cultivation in California. 



