272 FUNGOUS DISEASES OF PLANTS 



throughout Europe, Australia, and in some parts of Asia. The 

 commercial relations between the different countries have doubt- 

 less effected its very general distribution. In the United States 

 it has been known for nearly half a century, although it is un- 

 likely that it was a matter of commercial importance prior to the 

 general and widespread development of orcharding, and the con- 

 sequent more or less contiguous orchard areas. Certainly for 

 twenty years it has been recognized as of serious economic 

 importance in the central area already designated. 



Climatic relations. Evidences of the effects of the bitter rot 

 fungus are usually found in July and August, although in the 

 case of early summer apples in the far South, and under ex- 

 ceptionably favorable conditions, it may appear much earlier. 

 In common with most fungi, the favorable conditions are to 

 be found in warm, sultry weather accompanied by rains, condi- 

 tions so frequent during August in the chief bitter rot regions. 

 During seasons thus characterized the fungus may spread with 

 alarming rapidity, causing enormous devastation within a period 

 of a single week, — this length of time being therefore sufficient 

 under such circumstances for the propagation of the fungus 

 probably through two or more generations. Von Schrenk states 

 that the time of the appearance of the bitter rot is probably 

 influenced by the following factors: (i) age of the fruits; (2) 

 temperature and humidity of the air ; (3) presence of spore- 

 distributing centers. The canker areas of the twigs are said to 

 develop somewhat earlier in the season and under less restricted 

 conditions. During cold, dry summers the apple is notably free 

 from bitter rot, even though the fungus may have been un- 

 usually common the previous season. Cold weather may act 

 either as a preventive or as a check to the development of the 

 disease after a favorable season for infection. 



Losses. It would be impossible to state the average loss sus- 

 tained by the apple-growing industry throughout the United 

 States as a result of the ravages of this fungus. During years 

 when the disease is prevalent the loss will certainly amount to 

 millions of dollars. The president of the National Apple Grow- 

 ers Association estimated the losses in 1900 at $10,000,000. 

 Burrill reported for the same year a loss in four counties in 



