TROPICAL FRUITS 



187 



to $1,250,000 annually. Careful investigations of G. H. 

 Powell and his assistants have shown that the chief 

 trouble results from handling the fruit in such way as to 

 wound it, and thus provide an entering point for the fungus. 

 Without mechanical injury no decay from blue mold can 

 occur. Hence the only method of control that is necessary 



fiG. 80. — Two 



ight, P. digita- 



is painstaking care in handling the fruit to prevent bruising 

 or puncturing the skin. 



Black rot (Alternaria Citri Pierce). — This disease was 

 described and its cause given by Pierce in 1902. It attacks 

 only the navel orange, causing from 2 to 5 per cent loss 

 of the whole crop. It is easily recognized by the prema- 

 ture ripening which it induces, and by the deep red color 

 and extra large size of the fruit. The diseased fruits are 

 very conspicuous on the trees before the main crop has 

 colored. 



The spores of the fungus that causes the decay gain en- 



