Shamel: Washington Navel Orange 



441 



time there arc about 100,000 acres of 

 this variety cultivated in the State. A 

 typical Washington navel orange is 

 shown in Fig. 3; a typical productive 

 form Washington navel tree is shown in 

 Fig. 4; and a typical Washington 

 navel orange grove near Riverside, 

 Cal., is shown in the frontispiece. The 

 crop of navel oranges is about 25,000 

 carloads of fruit each year, containing 

 about 10,000,000 boxes of oranges. 

 From California, trees of this variety 

 have been sent to Japan, Australia, 

 South Africa, and other foreign citrus 

 districts. In those regions the variety 

 has become commercially important 

 and its culture is being rapidly extended, 

 so that it is becoming one of the leading 

 citrus varieties of the world. The 

 Washington navel orange in California 

 has been the foundation upon which 

 the citrus industry as a whole has been 

 developed. 



METHODS OF PROPAGATION 



The methods of propagation of the 

 Washington navel orange in California 

 are similar in many respects to those 

 practiced at Bahia. In California the 

 variety is usually budded upon stocks 

 from the Mission Sweet Seedling orange. 

 In some districts it has been propagated 

 upon stocks grown from grapefruit, the 

 Florida sour orange, and the Florida 

 rough lemon seeds. 



TYPES FROM BUD MUTATIONS 



In 1909 the writer began a series of 

 observations on the behavior of this 

 variety under different soil and climatic 

 conditions in California. In the study 

 of these trees, it was found that numer- 

 ous diverse types of trees and fruits 

 existed. Some of the striking types of 

 trees were distinguished by their habits 

 of growth, density of foliage, and other 

 easily discernible characteristics. A 

 close study of some of the trees dis- 

 closed the fact that they bore character- 

 istic fruits. The variation in these 

 types of the Washington navel orange, 

 both as regards trees and fruits, was so 

 marked that it was thought for a time 

 to be due to a mixture of varieties. 

 Later it was discovered that frequently 



trees grown from a single navel orange 

 bud produced several characteristic 

 types of fruits. In some cases this 

 variation was found to occur as limb 

 sports, in which case both the fruits 

 and foliage on these sporting limbs were 

 characteristic of the types to which they 

 belong. In other cases these variations 

 were found as single fruits. 



IMPORTANCE OF TYPES 



Systematic investigation of this sub- 

 ject was begun about this time for the 

 purpose of discovering the extent and 

 importance of the diversity of types 

 arising from bud mutations. Plots of 

 about 100 trees each were selected in 

 representative orchards and careful per- 

 formance records secured from each 

 tree in these plots. After six years' 

 systematic study, conclusions can be 

 safely drawn as to the significance of 

 bud mutations and the importance of 

 the types of the navel orange originat- 

 ing from these mutations. It has been 

 proven that the diverse types of the 

 navel orange existing in the California 

 orchards have originated from bud 

 sports. The trees of these types have 

 characteristic habits of growth and the 

 fruits borne by these trees are of very 

 widely differing commercial value. 



FREQUENCY OF BUD MUTATIONS 



The occurrence of these diverse types 

 is very much more frequent than has 

 heretofore been supposed to be the case. 

 They are of great and vital importance 

 to the growers from a commercial 

 standpoint. One of the characteristics of 

 some of the unproductive and undesir- 

 able types of trees is unusual vigor of 

 growth. Frequently these trees stand 

 out in orchards several feet in height 

 above the neighboring trees and have a 

 spread several feet in excess of that of 

 the standard tree. These inferior trees 

 also frequently produce an unusual 

 number of so-called suckers, or very 

 vigorous vegetative growth, which has 

 heretofore been highly prized for pro- 

 pagation. As a result of this condition, 

 there is little doubt but that in the 

 successive propagations of the past 

 years, an increasingly large proportion 



