184 



SCIENCE 



[N. S. Vol. XXVI. No. 658 



petioles and midribs of the common apple are 

 also brown and sunken and contain one to 

 several pycnidia, the spots occasionally coal- 

 escing. 



The appearance of the fungus on the fruits 

 of both the crab-apple and the common apple 

 is similar and the effect is much the same. 

 There are brown spots on the fruits, from one 

 fourth to one half an inch in diameter, with 

 a few to as many as fifty black pycnidia near 

 the center of the spots, the spots often coal- 

 escing. The fungus prevents the further 

 growth of the fruit in the infected area. The 

 tissue becomes shrunken and firm and cracks 

 are formed around the spots. This spotting 

 of the common apple is the same as the dis- 

 ease described by Clinton' in 1902, under the 

 name of "fruit-blotch {Phyllosticta sp.)," and, 

 in considerable more detail, by Scott and 

 Quaintance'' in a bulletin recently issued by 

 the United States Department of Agricul- 

 ture. 



Finding the fungus on the petioles of the 

 common apple suggested the possibility th.at 

 it might also occur on the branches. A search 

 was at once made for it on a tree where it 

 had previously been found on the petioles and 

 fruits and it was found on both the yearling 

 and older branches. It was more in evidence 

 on the " water sprouts " and on the branches 

 growing in partial shade than on those ex- 

 posed to the direct sunlight, not only on this 

 tree, but on others in the same orchard. The 

 next day the fungus was found on the 

 branches of the wild crab-apple tree where 

 the first specimens of it were collected on the 

 leaves and fruits. 



On the twigs of last year's growth, there 

 are light brown, flat, elliptical spots from one 

 fourth to one half an inch in diameter, con- 

 taining from a few to twenty to thirty black 

 pycnidia. The bark is usually cracked and 

 raised around the edge of the spot, giving it 

 the appearance of a small canker. On the 



' Clinton, George P., " Apple Eots of Illinois," 

 Univ. 111. Bui. 69: 190-191, February, 1902. 



' Scott, W. M., and Quaintanee, A. L., " Spray- 

 ing for Apple Diseases and the Coddling Moth in 

 the Ozarks," U. S. Dept. Agr. Bui. 283: 14-18, 

 April 29, 1907. 



older branches the fungus grows out from the 

 original spot and forms pycnidia around it. 

 The formation of pycnidia outside of the 

 point of primary infection in successive yeara 

 indicates that the fungus is perennial and that 

 it winters over on the branches. Pycnidia 

 were developing this spring at about the same 

 time that the apple trees were beginning to 

 show signs of activity. After pieces of the 

 infected twigs had been in a moist chamber a 

 few days, small white masses of spores began 

 to ooze out of the pycnidia. These spores 

 germinated when seeded in a synthetic-agar 

 culture medium and a mycelium developed. 

 Infection of the leaves and fruit during the 

 spring and summer is probably brought about 

 by the spores that develop in the cankers on 

 the branches. 



The spots on the pietioles, fruits, twigs and 

 branches are much alike in size and general 

 appearance, but they are five to ten or more 

 times larger than the spots on the leaves of 

 the crab-apple and the number of pycnidia in 

 them is many times greater. 



Several investigators, including those al- 

 ready referred to, seem to agree that the 

 " fruit-blotch," " apple-blotch," " dry-rot," etc., 

 is caused by a species of Phyllosticta, but 

 what species is not indicated. The fungus as 

 it occurs on the leaves of the wild crab-apple 

 furnishes a clue for its determination. In 

 1895, Ellis and Everhart" described and named 

 a fungus occurring on the leaves of the same 

 host as Phyllosticta solitaria E. & E., which 

 in all probability was the same as the one 

 under consideration. Both have the " spots 

 minute, 1 mm., round, pale white with a 

 darker border. Perithecia epiphyllous, soli- 

 tary, one in the center of each spot, Y5 ^ 

 diam. Sporules sub-globose, hyaline, nucleate, 

 5-6 fi diam.," and, in addition, those col- 

 lected by the writer have many of the spots 

 brown and the pycnidia (" perithecia ") and 

 spores larger. There is a considerable varia- 

 tion in the size of the pycnidia on the same 

 leaf and of the spores in a pycnidium. The 

 spores found by the writer range from 

 5-6 X 6-9 /*, the smallest being about the 



•Ellis, J. B., and Everhart, B. M., Proc. Phil. 

 Acad., 430, 1895. 



