4 BULLETIN 623, U. S. DEPARTMENT OF AGRICULTUKE. 
marked and important characteristic differences. The term ' 'strain' ' 
as here used designates a group of individuals of a horticultural 
variety differing from all other individuals of the variety in one or 
more constant and recognizable characteristics and capable of per- 
petuation through vegetative propagation. 
One of the theories most frequently advanced to account for the 
tree and fruit variations observed in the orchards was the possibility 
that the roots of such trees, or some of them, might be in so-called 
''soil pockets," or be influenced by other local soil conditions. The 
orchards hi which the investigational performance record plats are 
located are situated on narrow mesas between low hills and a deep 
arroyo. The soil of these mesas is decomposed granite which has 
been washed down from the hills. A great number of soil analyses 
were made of samples secured within the areas covered by the root 
systems of trees of all the strains under observation, and such areas 
were found to be very uniform in character and composition. 
The influence of the stocks upon the scions was suggested as an- 
other possible cause of the frequent variability observed, but this 
idea was proved to be erroneous by the discovery of numerous cases 
where some of the most distinct strains were found in the same tree 
grown from a single bud and therefore upon the same individual 
stock. Later it was discovered that in the case of these diverse 
bud variations occurring hi the same tree grown from a single bud, 
it was possible to isolate each of the important strains through bud 
selection in propagation, proving that the differences observed were 
true cases of bud variation. 
This variability of the trees and fruits of the Washington Xavel 
orange is of fundamental significance from the standpoint of the 
fruit grower and in any study of the conservation and the stabiliza- 
tion of the variety as a whole. In the product of some groves, many 
oranges are found to be so poor as to be wholly unfit for the market. 
This condition frequently has been due to the presence of trees of 
inferior strains in the groves. These inferior trees reduce the returns 
from the grove in some cases to a point where from this cause alone 
it is maintained at a loss. Many of the existing trees of the variable 
strains show unusually strong vegetative growth but a low produc- 
tion of fruit, which is of inferior commercial value. The poor com- 
mercial quality of this fruit is due in part to the following causes: 
Irregular and peculiar shapes not adapted to a proper arrangement 
in the ordinary commercial packages; undesirable and unattractive 
color; rough, ridged, corrugated, or ugly and uneven surfaces of the 
rinds ; very thick peel; a large amount of coarse rag ; a small amount of 
juice or juice of a sour and bitter flavor; or other fundamental inferior 
fruit characteristics. Trees of some of the strains were found to 
bear extremely large fruits, and in other instances very small fruits, 
