New York Agricultural Experiment Station. 389 



chards which is based on the results of those experiments. The 

 reader who cares to follow the subject further will find on the 

 following pages an account of the nature and appearance of the 

 disease and a somewhat detailed statement of the plans of the 

 experiments and the results which they brought forth. 



It has already been stated that the plum leaf-spot is due to 

 a fungus, Cylindrosporium Padi, Karsten, which attacks all kinds 

 of cultivated plums, including the native and Japanese sorts; 

 also cherries and some other kinds of stone fruits. It is quite 

 widely distributed in Europe and America. 



Appearance. 



In the plum orchard it makes its appearance soon after the 

 first leaves are full grown. The leaves begin to show little dis- 

 colored spots, at first about a sixteenth of an inch in diameter, 

 with margins often tinged with purple or red. As the disease 

 progresses the spots enlarge till they are an eighth of an inch 

 or more across. Larger spots may be formed by the coalescing 

 of several small ones. The spots soon become dark brown with 

 a pale center. The tissues wither, and frequently breaking away 

 from the healthy portion of the leaf which surrounds them, they 

 drop out and leave circular holes in the leaf, as illustrated in 

 plate XXIX, which is reproduced from a photograph of diseased 

 leaves. The holes thus formed are often as clean cut and clearly 

 defined as though they had been made with shot, and on account 

 of this characteristic the disease is sometimes called the shot- 

 hole disease. Inasmuch as another disease which attacks apri- 

 cots, almonds and other stone fruits is popularly known, especi- 

 ally in California, as the shot-hole disease, it is better to desig- 

 nate the trouble which we are discussing as the leaf-spot dis- 

 ease of plum and cherry. The holes which are formed in the 

 leaves by this disease are not always circular in form, but when 

 several spots coalesce into one, or when the disease finds ex- 

 tremely favorable conditions for rapid development, large 

 patches, irregular in shape, may drop from the leaf, giving the 

 foliage a ragged or worm-eaten ai)peurance. 



