172 
IOWA ACADEMY OF SCIENCE 
Assimilation of C0 2 by Laurel Leaves. 
Exp. No. 
Source of 
Leaves 
Area of 
Leaves 
Intensity of 
Light 
Hourly Mean 
Temperature 
Total CO a 
Assimilated 
CO a Assimil 
at’d perlOsq. 
in. per lOhrs. 
Station* 
Sq. in. 
Cc. N-10 
Iodine 
O 
Milligrams 
Milligrams 
i 
9 
36.21 
1.22 
10.8 
21.56 
5.95 
9 
9 
23.5 
3.40 
17.6 
40.48 
17.20 
S 
9 
23.52 
1.0 
13.7 
36.08 
11.51 
9 
28.64 
2.8 
17.6 
47.21 
13.52 
16.43 
2.8 
17.6 
2.64 
1.56 
*S'a. 9— Residential Centers. 
Sta. 4— Industrial Center. 
These authors carried on additional experiments to ascertain whether 
the soil played any role. To secure data upon this particular phase of 
the question, they grew timothy plants and watered them with rain 
water taken from the various stations. In the industrial centers they 
found that chemical analysis revealed a smaller protein content and a 
greater amount of crude fiber. In addition they also ascertained that 
an indirect effect was produced by a decreased bacterial acitity in the 
soil. 
Cohen & Huston (10) in their recent book “Smoke — A Study of Town 
Air” have here made a more exhaustive study of conditions at Leeds. 
The essential results derived at are practically the same. 
In the United States the contributions upon this subject are not as 
extensive as in Europe. Buckhout (11) in 1900, published an account 
on the effect of gases and smokes upon vegetation. His results are 
similar to those recorded in the earlier work of Schroeder and Reuss. 
Widtsoe (13) studied the effect of smelter smokes upon vegetation in 
the vicinity of the Highland Bay Smelter at Murray, Utah, belonging 
to the Utah Consolidated Mining Company. He found that the white 
pine was killed for a distance of seven miles as a direct result from the 
emission of S0 2 . In an analysis of fifty different soils in the smelter 
region, the amount of sulphuric acid present was not different, from 
the acid content in normal soils. 
By far the most extensive work in America has been done by H. K. 
Haywood (17) of the U. S. Department of Agriculture, Bureau of 
Chemistry. His results as ascertained from his first study show that 
the vegetation about a smelter is killed for a considerable distance. He 
attributes the cause to sulphur dioxide. Even if this gas is in small 
quantities, yet in time the effect is noticed and there is in addition an 
increased sulphur trioxide content of the leaves when put to a chemical 
