138 MANUAL OF FRUIT DISEASES' 



and en route to eastern markets. Fruits leaving the Pacific 

 Coast in good condition may show objectionable spotting when 

 placed on sale in the East. This peculiarity of the disease has 

 impaired the commercial standing of the Jonathan to no small 

 degree. 



Symptoms. 



The spots may appear while the fruit is still on the tree, or 

 after it has been picked. In the latter case they may develop in 

 transportation or in storage. The spots are frequently in great 

 abundance. A characteristic lesion may be described as fol- 

 lows : rarely more than one-eighth to three-fourths of an inch 

 in diameter, it is circular in shape ; the color is light-brown at 

 first and with some varieties it remains so for a long time, in 

 consequence of which the spot is inconspicuous. On red varie- 

 ties the color darkens very early in the development of the lesion. 

 The surface of the affected area is abruptly but slightly depressed. 

 The affected tissue is dry and often only the skin appears to be 

 discolored. In contrast to other fruit-spots it is more super- 

 ficial than bitter pit, New England fruit-spot, and young bitter- 

 rot lesions. 



Cause. 



The cause of Jonathan-spot is not certainly known. Several 

 theories and opinions are held in explanation of the causal 

 nature. Some believe that the disease is non-parasitic ; others 

 are of the opinion that a species of fungus, an Alternaria, is respon- 

 sible ; and still others champion the opinion that gas causes the 

 trouble. It may be safely stated that none of these ideas and 

 theories are based on conclusive proof. It is very possible that 

 two kinds of spots may occur together on the same fruit ; one 

 of which is non-parasitic in nature, and the other caused by 

 some fungus, possibly the one already mentioned. Further- 

 more, gases such as formaldehyde, sulfur and ammonia may 

 produce spots which are at present indistinguishable from those 

 of fungous or non-parasitic origin. Ammonia from the cooling 



