28 BULLETIN 395, U. S. DEPAETMENT OF AGRICULTURE. 



torily overcome (1) by conducting the experiments upon clean young 

 trees and nursery stock in a section (Madison, Wis.) in which peach 

 scab has not been observed to occur naturally, and (2) by using potted 

 trees which could be placed at will under controlled conditions and 

 by constructing moist compartments about young trees in the field. 



METHOD OF INOCULATION. 



The inoculations, unless otherwise stated, were made upon potted 

 1-year-old nursery trees which had been cut back to whips, from 

 which vigorous young branches developed in the normal fashion in 

 the spring. The sources of inoculation were 10-day-old to 20-day- 

 old Lima-bean agar cultures of single-spore strains of Cladosporium 

 carpopliilum isolated, respectively, from the fruit, twigs, and leaves of 

 the peach. In each experiment, parallel germination tests demon- 

 strated the viability of the spores used. The sporiferous suspensions 

 were prepared with sterile distilled water, as in the case of the fruit 

 inoculations, and were applied either as spray by means of sterile 

 De Vilbiss atomizers or by means of clean new camel's-hair brushes. 

 Each series was adequately controlled by plants treated in every 

 way like those inoculated except that sterile distilled water was 

 substituted for the sporiferous suspensions. Just after inoculation 

 the experimental plants were placed in a practically saturated atmos- 

 phere in a specially constructed moist compartment in the green- 

 house, and 2 to 10 days later they were transferred to the pathological 

 garden, where the pots were sunk to the level of the soil. In order 

 to obtain data regarding the spread of the disease in the field, the 

 plants were arranged in line, according to the sequence of their 

 experimental numbers, being placed far enough apart to avoid con- 

 tact. They were carefully cultivated and noted at frequent inter- 

 vals throughout the season. The results are briefly outHned below 

 (PL VI, figs. 1 to 5). 



Experiment 1, May 22, 1914.i 



Sources of inoculation. — Cladosporium carpophilum: (a) Fruit strain, (6) twig strain; 

 both from 13-day-old cultures. 



Methods. — This experiment was conducted in the pathological garden on 3-year- 

 old Elberta trees, numbered 851 to 854, which had been cut back to whips and had 

 put out numeroiis vigorous shoots, averaging about 6 inches in length. The inocu- 

 lations, except No. 854, were made by spray. The treatments were: No. 851, control; 

 No. 852, tmg strain; No. 853, fruit strain; No. 854, twig strain. On three branches 

 of No. 854 only the upper surfaces of the leaves were inoculated, and on three others 

 only the lower surfaces, the sporiferous suspension being applied with a clean new 

 camel's-hair brush. The twigs bearing these leaves were also inoculated. Each 

 experimental tree was covered by a large bell jar or a specially constructed glass box. 

 These devices were lined with wet filter paper and blocked up on temporary platforms. 

 In each of these moist compartments a jar of water maintained a high humidity. 

 On the afternoons of May 23 and May 24 the trees were sprayed lightly with sterile 



1 For further details of each experiment, see tlie methods of inoculation previously described. 



