

other as regards their temperature relations. 



Another reason for selecting these four citrus parasi- 

 tes, was the suggestion that their pathogenic activities might 

 be influenced by climatic temperature conditions. It was 

 thus possible that a study of their temperature relations 

 might tnrow light upon methods of combatting teem. General 

 observations in connection with many diseases due to plant 

 parasites have indicated that temperature is a very important 

 factor in their prevalence in any given season or in any giv- 

 en region. ... E. Stevens^ 3 ' nas shown that the rate of i 

 crease in diameter of cnestnut blight cankers is closely 

 related to temperature. Edgertcr/ 4 ' has emphasized the ap- 

 parent relation of temperature conditions on tne cccurance 

 of certain plant diseases in subtropical climates. He is 

 convinced that the absence of anthracnose in beans grown at 

 certain seasons in Louisiana. is due to the fact that the 

 average temperatures for the seasons when the disease is ab- 

 sence" are too far above the optimum for the growth of the 

 pathogenic fongus. The writer' 5 ^ has previously referred 

 to the limited geographical distribution of melanose due to 

 Phomopsis citri , one of the fungi here studied, and has sug- 

 gested that temperature conditions may be among the important 



(3) Stevens, 17. E. The influence of temperature : .e 

 growth of Endothia parasitica. Amer. Jour. Pot. 4, 

 112-118, 1917. 



(4) Edgerton, C. W. Effect of temperature on Glomerella. 

 Phytopathology 5 : 247-259, 1915. 



(5) Fawcett, H. S. The geogrophical distribution of the 

 citrus diseases , melanose and stem-end i . tins 

 Hopkins University Circular, Inarch, 1317, p. 338-391. 



