IOWA ACADEMY OF SCIENCE 
177 
but the opinion that the injury was due to smoke was substantiated 
when the trees were examined in August, At that time they were 
covered with dust and soot particles. The branches are rather short, 
distorted and the bark appears unusually thick. As there are a large 
number of outcropping rocks, one would naturally expect that here, 
lichens would have a great foothold. But none are found; the rocks 
are entirely free from them. The smoke* was again the critical factor. 
A similar situation is met with in a survey of the metropolis of Iowa. 
In proceeding on 93d St,, toward the Illinois Steel Co.’s works, the 
number of tree species falls: the red oaks, the burr oaks, the elms, the 
cottonwoods, the willows, drop out in succession. This is not true of the 
territory near the Illinois Steel Co. alone, but a similar situation is met 
with in the territory in the vicinity of the ‘Wisconsin Steel Co., and the 
In dian d Steel Co.’s Works at Indiana Harbor. The trees that are 
planted have a hard struggle for existence. The Baldwin Locomotive 
Works, the Pullman Oar Works, all show similar conditions; near the 
American Brake Shoe and Foundry Co., the cockle burs in close 
proximity were covered with a hard tarry substance, which could be 
pared off with a knife. A good sized silver poplar (Populus alba L.) 
was found in the same locality, as the cockle burs, and it apparently 
was not affected by the smoke even if there was sufficient material of 
tarry, greasy nature to leave a permanent impression on the back of 
the hand where the under surface of the leaf was pressed against it. 
At Whiting in the vicinity of the oil refineries of the Standard Oil Co., 
the vegetation is almost normal. The only outstanding feature was 
that the cat tails were dried further back, at that time of the year than 
is usual. This point would lead one to conclude that smoke generated 
from crude oil is not as harmful as smoke from coal. No doubt this 
is closely correlated with complete combustion. 
The chemical works near Hegewiseh show the results of a continued 
application of smoke from the coal consumed as well as the fumes from 
the chemicals manufactured. At this place the gases emitted have caused 
the tops of the oaks and willows to become dead. The trees in the 
direction of the prevailing winds are alone affected. Those on the oppo- 
site side are practically intact. At Gary, Indiana, the center of the 
U. S. Steel Co., the conditions are not 'well marked. The leaves of a 
basswood tree near the office had leaves that were of a dark brown color 
as early as in June. 
♦First noted by Dr. Henry C. Cowles of the University of Chicago. This in- 
formation was given in a verbal statement. 
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