IOWA ACADEMY OP SCIENCES. 
165 
frequently planted. There are several specimens in Fdifferent 
parts of the Agricultural college grounds, some of them stand- 
ing in close proximity to apple trees. Gymnosporangium 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 one species of Gymnosporangium and only one 
species of Roestelia at Ames. A second species of Gymnos- 
porangium, G. glohosum, Pari., has been found but once by 
Professor PammeT. 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 Phms coronaria is so generally affected with 
Rcestelia 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 Boestelia. It is well known that the range of some fungi is 
limited by slight differences in climate; for example, the 
potato-blight fungus, PJiytopMliora 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 w^ay to account for the facts is to suppose that cer- 
tain 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. Fwst, 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; 
seeond, 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 
7 Journal of Mycology, Vol. VII., p. 103. 
8 A Preliminary List of the Parasitic Fungi of Wisconsin, p. 29. 
