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University of California Publications in Agricultural Sciences [Vol.3 



is more irregular, jagged and rough (pis. 34 and 37) in the interior 

 valleys than in the coast districts, where the navel formation is much 

 more commonly smooth or submerged and closed. This imperfect and 

 open condition of the navels in the interior valleys, as will be brought 

 out later, is due to the harsher environmental complex to which the 

 fruits are subjected during the growing period. Everyone is familiar 

 with the fact that fruits borne in exposed positions, particularly in 

 the top of the tree, are very apt to be coarse and rough with large 

 protruding navels, while the interior fruit is much finer in texture. 

 The prevalence of Alternaria spores in the coast districts is certainly 

 not much less than in the interior valleys, but the amount of infection 

 is much less because of the smaller number of imperfect navels. 



As is shown in table 4, Alternaria spores are present on almost all 

 the styles, both in coast and in interior valley districts. In order to 

 ascertain whether infection occurred by the fungus growing down 

 through the style into the navel end, material known to be infected 

 with Alternaria was put up in paraffine, sectioned, and stained. 

 Although the fungus was conspicuous on the stigmatic surface no traces 

 of fungus mycelium could be found in the stylar tissues. This fact, 

 together with the fact that infection is definitely correlated with the 



