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 
