June lo, 1918 Experiments with Coccomyces spp. from Stone Fruits 567 



and consistently, and the latter with difficulty. P. munsoniana was 

 infected more readily by strains from P. cerasus than those from any other 

 source tried. While these strains induced fairly consistent and abundant 

 infection a prolonged incubation period always resulted, and the cross 

 appeared to be a rather difficult one. Infection on this host was induced 

 with still greater difficulty by strains from P. mahaleb, P. pennsylvanica, 

 and P. domestica. P. cerasifera was tested in only two instances (where 

 sprouts developed from Lombard stocks). Delayed infection resulted 

 in both cases, the inocula being, respectively, from P. cerasus and P. 

 pennsylvanica. A . persica was infected difficultly and only by inocula 

 from P. domestica. A. persica nectarina and P. armeniaca were tested 

 only in the experiments of 191 6, and with uniformly negative results. 

 P. besseyi was difficultly infected by inocula from P. cerasus, P. avium, 

 P. mahaleb, and P. domestica. The waxy cuticle of the leaves of this 

 species is very resistant to wetting. This fact may be in some measure 

 accountable for the inconsistency of results from the various tests on 

 P. besseyi. 



While, for purposes of summarization, it was deemed advisable to 

 omit from Tables IX and X details regarding the flecking and spotting 

 reported in Tables I to VIII, these apparently aberrant types of infection 

 should be given due consideration in the interpretation of the results of 

 these experiments. Although the confirmatory histological studies 

 necessary to justify conclusions have not yet been completed, this 

 flecking and spotting, in conjunction with the types of delayed infection 

 into which they merged, make it appear that various gradations of 

 infection may occur, ranging in all likelihood from mere penetration 

 of the germ tube to the production of typical, sporulating lesions. This 

 condition presents many interesting problems, and appears to offer an 

 excellent opportunity for fundamental studies of specialization of para- 

 sitism and of the intimate relations of host and parasite. It is fully 

 realized, however, that, while more than a thousand inoculation tests 

 have been made, these problems are little more than defined. For their 

 material advancement much more extensive experiments will be neces- 

 sary. These should include tests in which individual strains of the 

 fungi are carried through many generations with the aim of determining, 

 if possible, whether experimental changes in host relations induce de- 

 tectable changes in parasitism. Such studies would bear upon the 

 possibilities of variation among strains of different ancestry on a given 

 host, and should include comparative tests of strains obtained from 

 various sections. In this work due consideration should be given to the 

 possibility of variations in the susceptibility of different varieties of host 

 species and of individuals within a variety or species. Furthermore, as 

 the greenhouse experiments have indicated, it would be of much interest 

 and value to trace the effects of certain variable factors, particularly 

 temperature and the vigor of the host plant, in relation to infection. 



