186 
IOWA ACADEMY OF SCIENCE 
4. The effect of smokes and gases upon the leaves of plants con- 
cerns itself mainly with the assimilation process. 
5. Certain species on account of their anatomical structure are 
more resistant than others. 
6. As a means of prevention for an industrial city like that of Des 
Moines, Iowa, it is proposed to put in smokeless furnaces with tall 
smoke stacks, which will dilute the*S0 2 to such an extent as to be harm- 
less to the vegetation in general. Where gaseous emanations are pe- 
culiar to the product manufactured, special condensing flues must be 
provided. 
7. The smoke from locomotives is largely prevented by careful fir- 
ing. The real solution lies in electrification. 
As a final conclusion I wish to express my thanks to Dr. William 
Crocker and Mr. Lee I. Knight of the University of Chicago, who first 
suggested the problem to me and who have given me assistance in 
all phases of the work. I am also indebted to Mrs. Mary Fairfield for 
assistance in the translation of the French, and to Miss Harriette S. 
Kellogg for the translation of the Italian. I am also grateful to Mr. 
Harry McNutt of the Public Safety Department of the city of Des 
Moines, who has given me every possible assistance in carrying on my 
survey in that city; to Dr. J. M. Greenman, formerly of the University 
of Chicago, but now of the Missouri Botanical Garden and Mr. E. E. 
Sherff, of the Curtis High School, Chicago, for their determination 
and verification of species of plants listed for the various zones; to Dr. 
George T. Moore. Director of the Missouri Botanical Garden, for the 
loan of reference works on the subject. 
BIBLIOGRAPHY. 
1. Rettstadt — Ueber die Einwirkung des Rauches der Silberhiitten im Ober- 
harz auf die Waldbaume. Allgem. Forst. u. Jagd. Ztg. 1845. 
2. Stockhardt A/ — Ueber die Einwirkung des Rauches der Silberhiitten auf 
die benachbarte Vegetation — Polytechn. Centralbl. 257. 1850. 
3. Gerardin — Einfluss von Leuchtgas auf die Promenaden u Strassenbaume. 
Jahresbr. f. Agrikulturchem 7; 199. 1864. 
4. Schroeder & Reuss — Die Beschadigung der Vegetation durch Rauch und 
die Oberharzer Hiittenrauchschaden. Berlin, 1883. 
5. Sorauer P. — Zeitschrift f. Pflanzenkr. 7; 15. 1897. 
6. Kny L.— Bot. Zeitung 29; 852, 867, 1871. Bot. Gazette 46: 259-276. 1908. 
7. Hasselhof u. Lindau. — Die Beschadigung der Vegetation durch Rauch 
Berlin, 1903. 
8. Molisch, H. — Plants and tobacco smoke. Umschau 15 No. 13 — Exp. Sta. 
Record 25: 225. 
