juneio. i9i8 Experiments with Coccomyces spp. from Stone Fruits 553 



from inoculations made under more favorable conditions. Consequently 

 such positive results are left out of account in computing the average 

 degrees of infection (Table IX, See footnote c, Table I). 



P. cerasus was uniformly abundantly infected (PI. 59, A), while on 

 P. mahaleb (PI. 56, C) the infection was only slightly less severe. In 

 the greenhouse, after prolonged incubation periods, P. insitiiia (PI. 56, B) 

 consistently developed infection, but this cross did not occur in the 

 field trials. With P. munsoniana (PL 56, D) similar results were 

 obtained. In 1916, after prolonged incubation (Table I), this cross led 

 to infection in the field. The single greenhouse test with P. ccrasifera 

 (PI. 56, A) led to delayed infection. On the other inoculated plants 

 and on the controls (PI. 59, B), no infection developed, though in the 

 greenhouse after prolonged incubation periods small spots developed in 

 considerable abundance upon P. domestica (PI. 56, E) and P. salicina 

 and flecks upon P. americana B. Similarly, flecks developed upon P. 

 pennsyhanica out of doors (see p. 544). In none of these cases, 

 however, did fructification of the fungus accompany these develop- 

 ments. 



DISCUSSION OP TABLE III 



No infection resulted from the first inoculation of series 102, and 

 only slight infection on P. cerastis \vas induced by the first inoculation 

 of series 14. From all the other inoculations moderate infection devel- 

 oped, but in no case was it severe. The causes of these variations are 

 not fully understood. It seems probable that this generally low degree 

 of infection was due, in considerable part at least, to a diminution 

 in the pathogenicity of the fungus in culture, since a single strain, 

 more than a year old, was used for all these experiments. Such reduc- 

 tion in pathogenicity, however, would not explain the differences in the 

 results of the first and the subsequent inoculations of series 102. It is 

 possible that temperature variations in the greenhouses during the 

 course of these experiments may have been an important factor, as 

 temperature diff"erences might well cause more conspicuous variations 

 in the case of a strain of reduced pathogenicity than with a virulent 

 strain. It should also be remembered that, owing to the failure of 

 P. avium stock to root, the original host was not included in these 

 tests. These matters, however, are subjects for further investigation. 



Infection occurred consistently on P. cerasus and P. mahaleb. None 

 of the other experimental plants were infected, though in certain cases, 

 after prolonged incubation periods, spots developed upon P. padus, 

 P. domestica, P. insitiiia, and P. munsoniana, and flecks appeared on 

 P. americana A and B and P. salicina. 



