PAPERS ON BOTANY 139 



SOOTY BLOTCH OF POMACEOUS FEUITS^ 



Arthur Samuel Colby, University of Illixois 

 i. inteoductiox 



Sooty blotch, and fly speck, which often accompanies 

 it, which are snlliciently ilhistrated by Figs. 1 and 2 to 

 make clear the meaning of these names, have been known 

 in a general way in this country for almost nine decades, 

 or since 1832, as the cause of a peculiar spotting or 

 ''clouding" of certain pomaceous fruits, especially apple 

 and pear. The names adequately describe the appear- 

 ance of these fungi, which are commonly found on the 

 fruit. Occasionally other parts of the plant are affected. 

 One or both fungi may be present on the same portion of 

 the host, while if both are found they may be near each 

 other or widely separated. The fungi may appear dur- 

 ing the latter part of the growing season except where 

 rainfall is scarce at that time. Such blemishes, while not 

 the cause of decay, usually do cut down very materially 

 the salability of otherwise good fruit. 



Xot"\\T.thstanding the conspicuous character of these 

 fungi and their general distribution, which has resulted 

 in numerous references to their occurrence and sugges- 

 tions for their control, there has been comparatively 

 little study to determine their morphology, and relation 

 to other fungi. Some authors have held that sooty blotch 

 is distinct from fly speck, others, that the two are merely 

 different forms or aspects of the same fungus. Such 

 opinions have resulted in much confusion, and a wealth of 

 misinformation, handed do^^^l from one publication to 

 another. In an attempt to clear up to some extent, such 

 a chaotic condition, a morphological study of sooty blotch 

 on pomaceous fruits was made by the Avriter. Brief men- 

 tion is made of sooty blotch as it has been noted on the 

 woody parts of other plants, in some cases with incidental 

 studies of the same, if needed to throw light on common 

 problems of morphology. 



1 The results presented in this article formed part of a thesis submitted 

 by the author to the Graduate School of the University of Illinois in partial 

 fulfilment of the requirements for the degree of doctor of philosophy in 

 botany, May. 1919. 



