50 
IOWA ACADEMY OF SCIENCE 
germinate readily only when they have been submitted to the atmosphere for 
the winter; that saltpeter fertilizer favors the development of rust. He cites- 
the experiments conducted in 1894 which was very favorable to rust, to show 
that varieties from American, Indian and other foreign sources, are parti- 
cularly subject to rust. The investigation carried on by the German Agricul- 
tural Society since 1892 shows that hybrids of the square head were a little 
subject to the disease and varieties like Dumel were comparatively free from 
rust. 
Eccoasceae Influenced hy Weather. Plum pocket (Exoascus pruni and E. 
communis), Peach curl {Exoascus deformans) are excellent illustrations of 
fungi influenced in their development by meterological conditions. Peach curl 
was destructive in Southern Iowa where peaches are grown; in 1907 many 
correspondents reported it as destructive. In 1908 there was little of it. Some 
trees in the vicinity of Ames showed much of it in 1907, the same trees in 
1908 had none of the fungus. Puffed branches or plum pocket {E. communis) 
was abundant in 1907 in many parts of the state. It was also reported in 190& 
but not nearly as destructive. The curl on oak was also common in places in 
this state in 1907. The season of 1907 will show somewhat unusual conditions. 
May was unusually cool with late frosts. These conditions seem to be very 
favorable for the development of these fungi. 
The senior author of this paper during the present season has had unusual 
opportunities for studying several of the Exoasci in the Rocky Mountains, 
from Eastern Colorado to Utah. In all of these places the Exoasci were abun- 
dant. The leaves of the Rocky Mountain oak {Quercus undulata) were much 
diseased at all points visited, Colorado Springs, Palmer Lake, Placerville,, 
Colorado, Salt Lake City, and several other points in Utah. 
The Exoascus cerasi on Prunus Yirginiana and P. Pennsylvanica was also 
abundant in Colorado and Utah. Hundreds ®f leaves were puffed out. One 
of the most destructive parasites is the Exoascus on the hard Maple {Acer 
grandidentatum) ; near Logan every tree had nearly all of its leaves spotted 
from the effects of this fungus. The forests looked blighted. Another common 
fungus is an Exoascus on the Quaking Aspen, which was common in parts of 
Colorado. 
The conditions in the mountains are unusually favorable for the develop- 
ment of these fungi. The evenings are always cool and the spring backward. 
It is not unusual in spring and early sjimmer for frosts to occur. The disease 
appears earlier at lower elevations and later at higher altitudes. 
January 
February . 
March 
April 
May 
June 
July 
August — . 
September 
October 
November 
December , 
Temperature in degrees 
Precipitation in inches 
1907 
1908 
Normal 
1907 
1908 
Normal 
27.9 
24.4 
23.5 
1. 
.52 
1.12 
34.9 
27.4 
24.7 
.84 
.86 
1.18 
40.7 
37.5 
33. 
.97 
.52 
1.61 
43. 
44.2 
44.2 
1.99 
.9 
1.99 
47.1 
49.1 
'52.9 
2.37 
2.19 
1.86 
58.1 
59.1 
61.4 
1.16 
.96 
1.54 
66.2 
65.6 
65.6 
2.40 
2.6 
1.96 
64.5 
65.1 
2.13 
2.07 
57.5 
58.3 
57.7 
5.75 
3.35 
5.71 
49.1 
43.1 
46.1 
.89 
5.97 
1.16 
33.4 
34.3 
.37 
.57 
25.9 
25. 
1.02. 
.95 
