IOWA ACADEMY OP SCIENCES. 165 



frequently planted. There are several specimens in [different 

 parts of the Agricultural college grounds, some of them stand- 

 ing in close proximity to apple trees. Oymnosporangium mac- 

 ropus is fairly abundant, the amount varying according to the 

 nature of the season as regards moisture. It is usually suffi- 

 ciently abundant to thoroughly inoculate the wild crab trees. 

 There is only oiie species of Gymnosporangium and only one 

 species of Roestelia at Ames. A second species of Gymnos- 

 porangium, G. globosum, Pari., has been found but once by 

 Professor PammeF. This species occurs in Wisconsin as indi- 

 cated by Professor Trelease^ and may be more common in 

 eastern Iowa. It has not, however, been found since and Pro- 

 fessor 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 Boestelia has been found at Ames. 

 This tends to simplify matters considerably. Were it not for 

 the fact that Pirus coronaria is so generally affected with 

 Bcestelia and so easily inoculated artificially, we would at once 

 conclude 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, PhytopMliora infestans, 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 cer- 

 taia 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 the facts. There 

 are two chief objections to it. First, the college orchard con- 

 tains a large number of varieties and it is a remarkable circum- 

 stance that they should all be Boestelia — resistant. However, 

 it should be noted that most of them are Russian varieties; 

 second, as a case of varietal differences in susceptibility to 

 fungus attacks, it is unparalleled. 



In the spring of 1894 we started some inoculation experi- 

 ments 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 



^Journal of Mycology, Vol. VII., p. 103. 



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



