170 
IOWA ACADEMY OP SCIENCE 
ment, whereby the vegetation in and about an industrial center, may be 
saved from a gradual elimination process, not by an added expense to 
the community, but by conditions that conserve the waste products for 
the manufacturer, and also conserve the health to sav nothing of the 
beauty of the town itself for the inhabitants. It will then be the pur- 
pose of this paper to show the application of these issues to a restricted 
area in an industrial center of the city of Chicago, 111., and also to cite 
some general features in connection with a survey made of the city of 
Des Moines, IowaJ. 
HISTORICAL. 
As early as in 1845, records show that smoke emitted from the smoke 
stacks of manufacturing concerns had an injurious effect upon vegeta- 
tion. Rettstadt (1) pointed out that forest trees in the vicinity of a 
silver smelter were injured. Stockhardt (2) a few years later confirmed 
this report. Girardin (3) found that illuminating gas had an injurious 
effect upon street trees. Schroeder & Reuss (4) employing sulphur 
dioxide and hydrochloride gases upon Carpinus, Alnus, Picea, and Acer, 
noted a destruction of the chlorphyll and a retardation of the photo- 
synthetic processes. In a later experiment these same authors using S0 2 
recorded a premature falling of leaves, along with a greater S0 3 con- 
tent. These same results were again verified by Stockhardt (2). Sorauer 
(5) using asphalt vapors, in contact with the rose and horse chestnut, 
has shown that brown discolorations along with an increased tannin con- 
tent are produced. Kny (6) demonstrated the injurious effect of coal 
gas upon the maple and linden. In 1903, Hasselhoff and Lindau (7) 
brought out in a book form a number of important statements 1 as to 
nature and means by which the injury could take place. They con- 
cluded: 1, that the action does not take place through the soil but is 
centered in the conditions of the atmosphere and the leaf itself; 2, that 
the plants vary with reference to their sensitiveness; 3, that plants 
allowed to remain for a considerable length of time in an atmosphere 
containing small amounts of S0 2 will in time show the effects; 4, that 
the stomata play no role in the absorption of sulphurous acids; 5, that 
there is a derangement in the water circulation by an increased loss of 
water; 6, that the interior of the cells show plasmolysis and a decrease 
in starch manufacture and finally a decomposition; 7, that a chemical 
analysis gives an index to injury. Molisch (8) has recently studied the 
effect of tobacco smoke upon various seedlings and found that they 
behaved as if they had been exposed to traces of illuminating gas. He 
