PEACH SCAB AND ITS COISTTKOL. 31 



usual type, always on tlie lower surfaces. No marked difference was observed in 

 the results tt'om inoculations upon tlie very young and tlie mature leaves. Sparse 

 infection developed upon the leaves of the tree inoculated with the leaf strain of 

 the fungus, though none was found upon the twigs. No disease developed upon the 

 controls. 



Experiment 5, July 11, 1914. 



Sources of inoculation. — -Cladosporium carpophilum: (a) Fruit strain (isolated from 

 an overwintered scabbed peach at Madison, Wis., May 11, 1914); (6) twig strain; 

 (c) leaf strain; all from 17-day-old cultures. 



Methods. — The experimental trees were potted Chili. One was inoculated by 

 spray with the fruit strain and one with the twig strain, whUe two were similarly 

 treated with the leaf strain. Three other plants were inoculated upon marked areas 

 with the twig strain, one upon the upper surfaces, one upon the lower surfaces, and 

 one upon both surfaces of the leaves. The areas to be inoculated were surrounded 

 by circles of India ink, and the spoiiferous suspension was applied in small drops 

 by means of a camel's-hair bmsh. The ink was allowed to dry before the inocula- 

 tions were made. Two plants were sprayed with sterile distilled water as controls. 



Results. — On the trees inoculated by spray with the fniit, twig, and leaf strains, 

 the disease developed typically and abundantly upon the lower surfaces of the leaves 

 and rather sparsely upon the twigs. The leaf strain occasioned slightly less infection 

 than the others, but materially more than in similar preceding tests. This increase was 

 probably due to the fact that special care was taken to have an abundance of spores 

 in the suspension used for this inoculation. On September 29 the tree inoculated 

 only upon the upper surfaces of the leaves showed no infection. On the tree inocu- 

 lated only upon the lower leaf sm-faces, 14 of 29 inoculated areas showed infection. 

 On the remaining inoculated plant, 66 of 98 inoculated areas on the lower surfaces 

 of the leaves showed infection, while no disease was evident upon 93 similarly treated 

 areas upon the upper sm'faces. No infection was observed except on inoculated 

 ajeas. The control plant developed no evidence of infection. 



EEISOLATION OF THE FUNGUS. 



Numeroiis microsco23ic examinations showed that Cladosporium 

 carpopJiilum was uniformly associated with the lesions produced by 

 inoculation. The fungus was reisolated from twig and leaf infections 

 induced by the fruit, twig, and leaf strains, respectively. The 

 morphological and cultural characters of the reisolated strains were 

 typical of 0. carpophilum. 



CONCLUSIONS. 



These experiments show (1) that Cladosporium carpopJiilum from 

 cultures of single-spore strains isolated from scab lesions on (a) 

 fruit, (b) twigs, or (c) leaves of the peach is capable of producing 

 abundant typical infection upon peach twigs and leaves; (2) that 

 natural infection of the leaves occurs chiefly, and apparently exclu- 

 sively, upon the lower (dorsal) surfaces; (3) that young or mature 

 leaves may be abundantly infected; (4) that the period of incubation 

 for leaf infection may vary from 25 to 45 days, and probably more, 

 depending upon conditions; (5) that the period of incubation for 

 twig infection approximates that for leaf infection; and (6) that 

 under favorable conditions secondary twig and leaf infections may 

 appear in the latter part of the summer. 



