6 BrLLZTIX 623. XT. 5. DEPARTMENT OF AGBICrLTTEE. 
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 Xavel 
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 Xavel 
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 
Xavel 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. 
