284 University of California Publications in Agricultural Sciences [Vol.3 



which in excessive amounts tend to retard vegetative growth, intensify 

 certain characteristics of the fruit which greatly enhance its market 

 value. Thus we find that the Bahia or Washington Navel variety of 

 Citrus sinensis has comparatively little commercial value at Bahia, 

 Brazil, where it originated, or in any other tropical country where it 

 has been tested. In a semitropical desert environment, however, this 

 variety of orange is high in sugar content, has skin characteristics 

 which lessen decay in transit, and is possessed of a deep reddish orange 

 color which increases its salability. For these reasons the cultivation 

 of oranges under arid and semiarid conditions has developed into an 

 industry of large importance, in which many millions of dollars are 

 invested and upon which many thousands of people are dependent for 

 a livelihood. 



When we consider the morphological characteristics of the more or 

 less xerophytic vegetation indigenous to the region now occupied by 

 orange orchards in California and note the striking dissimilarity 

 between the forms of native plants and citrus trees, we may reasonably 

 suspect that our orange trees may find it more or less difficult to adjust 

 themselves to the new and strange environment. Perhaps the under- 

 ground environment provided by soils which, on account of low rainfall 

 and consequent lack of leaching, still retain a large proportion of the 

 soluble salts resulting from the decomposition of soil minerals, would 

 be equally as disordered as the above-ground environment were it not 

 for the fact that water artificially applied by irrigation lessens the 

 asperity of the conditions met by the roots. Not only is the total 

 environmental complex to which our orange trees are exposed incon- 

 sistent with their natural requirements, but the trees of the Washing- 

 ton Navel variety are themselves decidedly abnormal. It is the 

 universal practice to place scions of the desired variety upon rootstocks 

 of other species of Citrus so that the reciprocal influences between 

 stock and scion come into full play. Moreover, the variety in question 

 bears some indications of hybrid origin. The blossoms are entirely 

 devoid of viable pollen, functional ovules are few, the fruits are 

 partially double, peculiar in structure and seedless, and the vegetative 

 parts exhibit an erratic polymorphism which has so far proved 

 decidedly puzzling. 



It is a matter of common observation that in the interior desert-like 

 valleys of the arid southwest the Navel orange is somewhat dwarfed 

 in stature, the leaves tend to persist to an unusual age, the volume of 

 bloom is abnormally large, shedding of the flowers and young fruits is 



