48 MISCELLANEOUS PAPEES. 



trees is small and of poor quality, and the fruit buds must necessarily 

 go into the dormant stage in a rather immature condition, often re- 

 sulting in a partial or complete failure of the next year's crop. 



CAUSE OF LEAF-SPOT. 



Considerable confusion has existed as to the cause of this leaf- 

 spot disease. Though no inoculation experiments have been reported, 

 the disease has generally been conceded to be of fungous origin and 

 has commonly been attributed to PhyUosticta pirina Sacc, and less 

 commonly to PhyUosticta limitata Pk. and Sphaeropsis malorum Pk., 

 while species of Hendersonia, Pestalozzia, and other fungi have been 

 reported as occurring on the diseased areas. 



The disease in its economic aspect was first mentioned by Alwood 1 a 

 in 1892, when he described a " brown-spot " of apple foliage and re- 

 ported a serious outbreak in the Virginia orchards during the preced- 

 ing summer. He attributed the trouble doubtfully to PhyUosticta 

 pirina. 



In 1895 Kinney 2 cited the same fungus as the cause of apple and 

 pear leaf-spots in Rhode Island. 



Stewart, 3 in 1896, reported a serious outbreak of leaf-spot on Long 

 Island caused by an undescribed fungus which Peck named Phyl- 

 losticta limitata. 



In 1898 Alwood 4 again recorded the common occurrence of Phyl- 

 losticta pirina on leaf spots, but found Sphaeropsis malorum Pk. and 

 Hendersonia mali Thiim. associated with it. 



Lamson, 5 in 1899, gave PhyUosticta pirina as the cause of " brown- 

 spot " of apple foliage in New Hampshire, while Corbett, 6 in l^OO, 

 described a •" brown-spot," or " frog-eye," in West Virginia due to 

 the same fungus. 



In 1902 Stewart and Eustace 7 questioned the parasitism of Phyl- 

 losticta pirina and P. limitata. In their opinion "at least a large 

 part of the so-called apple leaf-spot is due to spray injury and weather 

 conditions and not to fungous origin." They suggest that the fungi 

 in question live saprophytically on leaves injured by Bordeaux mix- 

 ture and arsenical sprays, or in the case of unsprayed trees on leaf- 

 spots which are in some way the result of atmospheric influences. % A 

 possible explanation for the formation of the spots is " when a 

 shower is followed by bright sunshine, drops of water on the leaves 

 act as lenses and concentrate the sun's rays to such an extent as to 

 overheat the tissues underneath." 



In 1902 Clinton 8 recorded Sphaeropsis malorum as the cause of 

 brownish spots on apple leaves in Illinois " much like those of the 



a The serial numbers used iu this paper refer to the bibliography, which will 

 be found on page 54. 

 121— Y 



