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



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 in 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 in the same tree grown from a single bud, 

 it was possible to isolate each of the important strains through bud 

 selection hi propagation, proving that the differences observed were 

 true cases of bud variation. 



This variability of the trees and fruits of the Washington Navel 

 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, 



