550 Journal of Agricultural Research voi. xiii. no. n 



been placed in the moist chamber by propping the leaves against adjacent 

 leaves or twigs (fig. 3). Ordinarily several cells were placed upon each 

 plant, and in order to increase the number of trials, they were moved at 

 suitable times to other leaves. By shifting the cells from one plant to an- 

 other within the series when these changes were made, the chances of fail- 

 ure of discharge of spores upon any given plant were minimized. Just be- 

 fore each experiment was begun, each leaf fragment of the ascogenous 

 material to be used was tested for spore discharge, and unless spores were 

 being discharged abundantly the material was rejected. Even with these 

 precautions, however, it was not possible to insure a satisfactory inoculum 

 in every case. Therefore, full confidence can not be placed in each in- 

 dividual negative result. Great care was exercised to maintain within 

 the cells favorable conditions of humidity for discharge of the asci. 

 The leaf fragments, bearing fresh, open ascocarps, were always taken 

 directly from the moist chambers. They were wet just enough to make 

 them adhere well to the cover glasses. A white string about the petiole 

 of each inoculated leaf served as a marker, and in each series all the 

 inoculations were made on approximately the same part of the leaf sur- 

 face, usually, for convenience, near the apex. Freshly discharged 

 ascospores were found to be so uniformly viable that in most cases special 

 germination tests were not made. The inoculated plants were held in 

 the moist chambers for two days, after which they were incubated in the 

 greenhouses. No inoculated plant or other source of possible inoculum 

 was carried into the greenhouse Vv'here the uninoculated plants were 

 grown, and the various inoculated series were kept well apart in the other 

 greenhouses, in order to minimize the possibilities of chance infection. 

 In these greenhouses throughout the early spring the temperatures 

 ordinarily ranged between 24° and 29° C. In late spring and early sum- 

 mer the maximum temperatures were considerably higher, but not ex- 

 cessive. In late July and August, despite careful attention to shading 

 and ventilation, the temperatures at times became excessive. The more 

 important aspects of the experiments, however, were completed before 

 this time. 



The control plants were sprayed with sterile distilled water, and held 

 in the moist chamber for two days. 



RESULTS OF EXPERIMENTS OF 1917 



The results of the experiments of 191 7 are summarized in Tables II 

 to VIII. 



Of the scores of control plants of both the outdoor and the greenhouse 

 series, including representatives of all the species and varieties used, not 

 one developed a single infection throughout the entire season. Futher- 

 more, the many inoculated plants upon which no infection occurred 

 serve as additional controls. It is evident, therefore, that the experi- 

 ments were adequately and satisfactorily guarded against chance infec- 



