184 
IOWA ACADEMY OF SCIENCE 
of tannin in the cells. Gaten has emphasized the accumulation of con- 
siderable cork deposit in the leaf petiole. 
The whole question as to the injury encountered is intimately con- 
nected with the subject of assimilation. The diminished illumination, 
the cutting off -of the C0 2 and 0 2 supply, the interference with the 
transpiration stream, the cutting down of the leaf surface through a loss 
of leaflets, change in position or by the formation of spotted alreas all 
show that normal photosynthesis does not occur. As the process is 
responsible for the storage food manufactured, the natural conclusion 
to be arrived at, is that insufficient food is manufactured. As food is 
stored from the base of the trunk upward, there is not always sufficient 
time to complete the storage up to the tips, when the laboratories are 
run with less than their normal supply of raw material. This point 
was emphasized in connection with the cross sections made of pine 
needles collected at Washington Park, Chicago. Where a leaf was en- 
tirely covered with the tarry mixture a considerable smaller quantity 
of stored starch was found than in a leaf which had not been exposed 
sufficiently to be coated. In making an examination of the growth 
rings it is noted that those of the smoke region are much smaller. This 
whole question then concentrates itself into one of food supply, and 
growth development. When there is not a sufficient amount of food 
manufactured, growth becomes less. The result of the insufficient 
amount of food causes a slow starvation. As a final result death occurs. 
PROPOSED SUGGESTIONS FOR REMEDY. 
It is not the purpose of this paper to give an account of extensive 
plans, that might aid in the cutting down of the smoke nuisance but 
a few suggestions might be appropriate. Concerns like the Illinois 
Steel Co., and Wisconsin Steel Co. will have to concern themselves 
with gaseous emanations from two sources; first, those coming as a 
by product from the ore, second, those coming from the stacks. Both are 
questions of economy. Some plan whereby the waste products as gases 
are condensed appears to be the only method for solution for the first. 
The other can to a large extent be solved by following out the laws 
necessary for complete combustion. Mechanical stokers to a large 
extent have helped to solve this part of it. 
For commercial or industrial centers like Des Moines, Iowa, the plan 
is to put in every plant of any considerable size mechanical stokers or 
devices that will give a complete combustion for the coal whereby C0 2 
and S0 2 alone, are produced. As Des Moines is situated in a low area 
