MAINE APPLE DISEASES. 359 



Leaf spot of the apple has been discussed by a large number 

 of writers and the cause attributed to a number of dilTerenc 

 fungi. In many cases the fact that a certain fungus was very 

 frequently found on the spots was taken as sufficient evidence 

 that it was the cause of the disease. Of recent years it has been 

 questioned whether the presence of a fungus on a leaf spot, no 

 matter how constantly it occurred there, should be taken as evi- 

 dence that the fungus caused the disease. It has been held that 

 it is necessary to isolate the fungus in pure culture and then pro- 

 duce the disease by inoculation under control conditions before 

 the matter could be definitely settled. In the summers of 19C6 

 and 1907 Scott and Rorcr* made a study of the disease in the 

 Ozarks in which they isolated fungi from leaf spots and carried 

 on inoculation experiments. Of the various fungi isolated 

 Stliacropsis rnalontm Pk., the same fungus which causes a de- 

 structive fruit rot (p. 362) and limb canker (p. 372 )in Maine 

 was the only one capable of causing the disease when its spores 

 were sprayed on the leaves. 



On account of the importance of the fungous leaf spot in 

 Maine it was thought desirable to make a thorough study of the 

 pathogenicity and interrelation of the various fungi found asso- 

 ciated with leaf spot, fruit decays, and limb cankers in this State. 

 The results of a part of this work have already been published** 

 and other parts will be publi.shed later. It is sufficient for our 

 present purpose to state that out of a large number of fimgi iso- 

 lated from leaf spot in Maine Sf'luirropsis inalonim was the only 

 one which would produce the disease on inoculation. 



The results obtained here, taken together with the conclu- 

 sions of Scott and Rorer and the work of Lewist in New 

 Hampshire would seem to indicate that Sphacrof^sis is the only 

 one of the fungi occurring so abundantly on the dead spots in 

 apple leaves which is capable of causing the disease in this sec- 

 tion of the country. 



* Scott, W. M.. and Rorcr, J. B., Bureau PI. Ind., U. S. D. A., Bui. 

 121, Part V, pp. 47-54. 1908. 



** Lewi's. C. E. Apple Diseases Caused by Coryucum foliirolitin ;.nd 

 Phoma tiioli. Me. Exp. Sta. Bui. 170. igog. A New Species of 

 Endoinyces from Decaying Apple. Me. E.xp. Sta. Bui. 178, 1010. 



t Lewis, Isaac M., N. H. Exp. Sta. Rep. 20, pp. 365-369, 1908. 



