CALIFORNIA CITRUS CULTURE. 49 



a decay of the crown or stem, while the second may produce dead spots 

 at any point. Improper soil (it should be sand, at least on top), over- 

 irrigation "and insufficient drainage are favorable to this disease. 



FIG. 24. Navel or black rot, Alternaria citri, infecting 

 the navel end. (After Amundsen.) 



Navel Rot (Alternaria citri). 



(Fig. 24.) 



This rot attacks only the navel orange. It is not a true parasite, and 

 attacks the navel end only when it is injured in growth. It is thought 

 that moisture in the navel cavity may favor the disease, as autumn rains 

 seem to increase the affection. The navel is the finest winter variety 

 for all around use, and its seedlessness adds to its excellence. This rot 

 is cne of its few drawbacks, but it is only occasionally that it becomes 

 of serious importance. 



Root Rot (Oak-root Fungus, Armillaria mellea). 



(Fig. 25.) 



AVhere orange trees and many others replace oak trees in the foothills 

 and valleys a toadstool fungus, which previously infested the roots of 

 the oak, may attack and greatly injure the trees. It is common in 

 California, and often serious. Mr. Earl Morris, county horticultural 

 commissioner of Santa Clara County, regards it as the most serious 

 pest in the orchards of his county at the present time. It spreads to 

 other trees from the center of infection. Professor Smith suggests that 

 in case this disease is troublesome other and more resistant trees, like 

 walnuts or cherries, be grown in their stead. I have seen one case of 

 4 cc 



