5'38 Report of the Mycologist of the 



Gymnosporangitmn macropiis is fairly abundant, the amount vary- 

 ing according to the nature of the season as regards moisture. It is 

 usually sufficiently abundant to thoroughly inoculate the wild crab 

 trees. There is only one species of Gymnosporangium^ and only 

 one species of Roestelia at Ames. A second species of Gyranospo- 

 rangium, G. globosum, Farl., has been found but once by Prof. 

 Pammel.'' This species occurs in Wisconsin, as indicated by Prof. 

 Trelease,^ and may be more common in Eastern Iowa. It has not, 

 however, been found since, and Prof. Pammel writes us that it may 

 have been a chance introduction from material sent to Dr. Halsted. 

 So far as we know, only one species of Roestelia has been found at 

 Ames. This fact tends to simplify matters considerably. Were it 

 not for the fact that Plrus coronaria is so generally affected with 

 Roestelia and so easily inoculated artilicially, we would at once con- 

 clude that the immunity of the cultivated apple is due to the climatic 

 conditions in Iowa being unfavorable to the growth of Roestelia. 

 It is well known that the range of some fungi is limited by slight 

 differences in climate ; for example, the potato-blight fungus, Phy- 

 tophthora iiifestans, De By., which causes great losses in some parts 

 of the United States, has, I believe, never been collected in the state 

 of Iowa. The climate there is too dry for it. 



Another way to account for the facts is to suppose that certain 

 varieties of apples are not susceptible to the disease, and that only 

 non-susceptible varieties are grown at Ames. This theory comes 

 nearest to accounting for all of the facts. There are two chief ob- 

 jections to it. First, the college orchard contains a large number 

 of varieties, and it is a remarkable circumstance that they should all 

 be Roestelia-Yeshtojit. However, it should be noted that most of 

 them are Russian varieties. Second, as a case of varietal differ- 

 ences in susceptibility to fungus attacks it is unparalleled. 



In the spring of 1894 we started some inoculation experiments at 

 Ames. Pirus coronaria., eleven varieties of cultivated apples and 

 the previously mentioned Tetofsky tree top-worked with Fluke 

 crab, were inoculated with the native G. macropus and with G. 

 raacropiis from Cambridge, Mass., communicated by Mr. B. M. 

 Duggar. All were complete failures. The spring and summer 

 were unusually dry. This probably accounts for the failures with 



7 Journal f Mycology, Vol. VII.. p. 102. 



8 A Preliminary List of the Parasitic Fungi of Wisconsin, p. 29. 



