PEACH SCAB AND ITS CONTKOL. 29 



distilled water, care being taken to allow no dripping. On May 29 the glass con- 

 trivances were removed. 



Results. — On June 20, 29 days after inoculation, abundant infections were barely 

 macroscopic on the twigs and on the under siirfaces of the leaves of Nos. 852, 853, 

 and 854, with the exception of those leaves of No. 854 which were inoculated only 

 upon their upper surfaces. These and the control plant, No. 851, developed no signs 

 of infection during the entii'e season, the last observation being made on October 18. 

 The progress of the disease is best followed in a typical example, as No. 854b. On 

 the inoculated twig surface on June 20 occasional infections were barely visible. 

 On July 1 about 20 infections less than 1 millimeter in diameter were observed. On 

 July 10 over 30 lesions were definitely visible, their diameters varying fi-om one-half 

 to 2 millimeters. On July 17, 46 lesions were counted, the maximal diameter being 

 3 millimeters. During this period and subsequently the twig grew very rapidly, 

 and bark formation began early. Consequently, the lesions developed but little 

 further and gradually lost their identity as the season progressed. Normally, how- 

 ever, it should be remembered, peach twigs of older trees do not cork over during 

 their first season's development, and on. such wood the scab lesions may continue to 

 enlarge during the following season. The progress of the disease on the leaves closely 

 paralleled that on the twigs, except that the lesions were considerably more numer- 

 ous, over a hundred frequently developing upon a single leaf. 



Experiment 2, June 6, 1914. 



Sources of inoculation. — Cladosporium carpophilum: (a) Fruit strain, (b) twig strain, 

 (c) leaf strain; all from 20-day-old cultures. 



Methods. — Three potted 1-year-old Elberta trees of the type previously described 

 were thoroughly sprstyed, respectively, with the three sporiferous suspensions. Two 

 others were inoculated with the fruit strain upon (a) the upper and (6) the lower leaf 

 surfaces, respectively, the sporiferous suspension being applied by means of a camel's- 

 hair brush. Two controls were sprayed with sterile distilled water. The experiment 

 was duplicated on Chili trees of the same type. Immediately after treatment the 

 trees were placed in the moist compartment in the greenhouse. After three days 

 they were sprayed lightly with sterile distilled water, and five days later they were 

 removed to the field. 



Results. — On the twigs and on the lower surfaces of the leaves of the trees sprayed 

 with the fniit and twig strains of the fungus, abundant infection was noted on July 10, 

 34 days after inoculation. The infections had probably been visible for several days. 

 The lesions increased rapidly in number throughout July. The twig lesions developed 

 slowly throughout the season, attaining a maximal diameter of 6 mm. by October 18. 

 In September and October scattered secondary infections appeared upon the younger 

 wood. The leaf infections typically developed as mere superficial flecks, averaging 

 1 to 2 mm. in diameter. In many cases, however, the leaf lamina above these flecks 

 became yellowed, and the most severely affected leaves fell in August and September. 

 In September and October scattered secondary infections developed, both on old 

 leaves and on foliage which was produced after the inoculations were made. 



On the trees inoculated with the leaf strain of the fungus no disease was observed 

 until July 24, when occasional lesions were noted on the twigs and on the lower sur- 

 faces of the leaves. Little further evidence of disease developed until the latter part 

 of the season, when a limited amount of secondary infection of the type above described 

 appeared. The sparseness of infection from this source is attributed to the fact that 

 this strain of the fungus sporulates much less vigorously than the others used. The 

 spores in the suspension with which these inoculations were made were observed to 

 be relatively sparse and to germinate with less than normal vigor. Since these char- 

 acteristics are not common to all strains of Cladosporium carpophilum isolated from 

 peach leaves, it is unfortunate that only this strain was available for these experi- 



