30 BULLETIN 395, U. S. DEPARTMENT OF AGRICULTURE. 



ments. However, the pathogenicity of other leaf strains was clearly proved in sub- 

 sequent experiments. 



On the leaves inoculated only on their upper surfaces no primary infection de- 

 veloped, with the exception of four lesions which appeared, closely gi'ouped, at the 

 margin of one leaf. This infection clearly occurred on the lower surface, and was 

 probably due to chance inoculation, such as might occur should a drop of the sporif- 

 erous suspension accumulate at the margin of the leaf and extend over the edge. 

 Wliile great care was taken to avoid mischance of this kind, as is attested by the 

 fact that only one other such case was observed throughout the season's work, it is 

 obviously impracticable to secure uniformly perfect results from extensive series of 

 experiments of this type. In September and October occasional secondary infections 

 appeared upon the under sui'faces of the leaves of these plants. 



Abundant disease developed on the lower sui'faces of the leaves which were inocu- 

 lated on these surfaces only. Its development paralleled that on the corresponding 

 sprayed plants. 



On the foiu' controls no disease developed, with the exception of occasional late 

 secondary infections upon the leaves and young wood of the plant which was placed 

 about a foot from one of the most severely infected trees of the series. This infection 

 did not becorae evident until October. The fact that the next control plant, about 

 a foot farther from the source of infection, developed no disease is of significance in. 

 relation to methods of spore dissemination, which will be discussed later. 



ExPEEiMENT 3, June 22, 1914. 



Source of inoculation. — Cladosporium carpophilum: Twig strain, from a 14-day-old 

 culture. 



Methods. — The inoculations were made upon potted Chili trees of the type pre- 

 viously described. Only the upper surfaces of the leaves of one tree were inoculated 

 by spray, while only the lower surfaces of the leaves of another were similarly treated. 

 A third plant was sprayed with sterile distilled water as a control. The subsequent 

 treatment of the experimental plants paralleled that of the preceding series. 



Results. — The leaves inoculated upon their upper sxu'faces developed no infection, 

 with the exception of several closely aggregated lesions on the lower surface near the 

 margin of one leaf. This infection clearly occmTed upon the lower siu'face and was 

 doubtless of similar origin to the parallel case discussed under experiment 2. On 

 the leaves inoculated upon their lower surfaces, abundant infection was noted on 

 July 17, 25 days after inoculation. The lesions had probably been visible several 

 days. On July 24 the lesions had increased materially in number and size, scores 

 of infections frequently occurring on individual leaves. By the end of September 

 most of the worst affected leaves had fallen. No infection had become visible upon 

 the control plant when it was last examined on October 18. 



Experiment 4, July 2, 1914. 



Sources of inoculation. — Cladosporium carpophilum: (a) Twig strain, (6) leaf strain; 

 both from 10-day-old cultures. 



Methods. — These inoculations were made upon potted Chili trees of the t>^e used 

 in the preceding experiment. One tree was inoculated only upon the upper leaf 

 surfaces with the twig strain of the fungus, another was similarly treated only upon 

 the lower leaf surfaces, and a third on both surfaces of the leaves. Very young and 

 mature leaves were separately marked and noted. Another plant was inoculated 

 with spray from the leaf strain of the organism, while two others were sprayed with 

 sterile distilled water as controls. The experimental plants were subsequently 

 accorded treatment similar to that of the preceding series. 



Results. — When the last notes were made on October 18, no infection had become 

 visible upon the leaves inoculated only upon their upper surfaces. Those inoculated 

 upon the lower surfaces or upon both surfaces developed abundant infection of the 



