THE EFFECT OF SMOKE AND GASES UPON VEGETATION. 
BY A. h. BAKKE. 
INTRODUCTION. 
The history of an industrial community marks itself into three di- 
visions: (1) the movement from the country into the city, (2) the 
building up of enterprises or commercial concerns, (3) the conserva- 
tion of waste products. The movement; of the people from the coun- 
try to the city carries with it a number of problems. Many of these 
would not be met with in the country. The earlier stages, with reference 
to this development, are not concerned with problems for the community 
as a whole. The pavement of streets, the erection of public buildings, 
other than school houses are not a part of the general program. Then as 
industries, under competition, endeavor to utilize a narrower selling mar- 
gin, there is a general movement, and in many cases instigated by the 
people at large, for a conservation of products that are a nuisance, or 
regarded as being detrimental to the health of the people, as well as the 
animals and plants of that community. Such considerations have lead 
to a condensation of the sulphur dioxide and arsenic trioxide in our 
smelters; such considerations are responsible for the condensing of the 
cement dust* in our cement plants: such considerations have led the 
manufacturers of Germany to utilize profitably as many of the waste 
products as they do, rather than to have them emptied into the atmos- 
phere as is ordinarily done under the first two periods. 
The smoke problem is a question that centers about the third state. 
In Germany and elsewhere on the Continent, the issues have long been 
presented. A. great deal of careful investigation is now being done in the 
city of Pittsburgh, Penn. Smoke has been considered a necessary evil. But 
experimental evidence is entirely against this conception. When it is 
understood that in burning of coal, incomplete combustion with its 
emission of toxic materials is a wasteful process to the manufacturer, 
and an obstacle to normal existence of animals and plants, the problem 
of smoke prevention will be successfully dealt with. This calls our 
attention to a consideration of another phase of the conservation move- 
* Plant World 13: 283-288. 
