420 BOTANICAL GAZETTE [JUNE 
H,SO, to soils would render a service to the plant different in de- 
gree only but not in kind from that rendered by the application 
of HNO. 
General remarks 
While we offer the results given above as a preliminary report 
merely, on a series of investigations which we trust will ultimately 
make a thorough survey of the subject, we must conclude from these 
data that the tolerance of plants for certain of the inorganic salts, 
commonly regarded as very poisonous, is much greater than we have 
been wont to believe. It is true that we have commonly accepted 
the idea that very small quantities of poisons may act as stimulants, 
but our results show that plants do not merely tolerate but are 
actually stimulated by quite considerable quantities of these toxic 
salts. It is very desirable, therefore, to arrive at a definite under- 
standing of the limits of toxicity of the substances in question, 
which we are now endeavoring to do. 
It would appear to us, further, that the results we have obtained 
are sufficient evidence to prove that a more thorough investigation 
into the effects of smelter wastes on plants is necessary before 
we are enabled to determine justly whether from that standpoint 
smelter plants are inflicting appreciable injury on the soils imme- 
diately surrounding them and on the soils of contiguous territory. 
Our results on the effects of MnSO, are considered of importance 
here both because of the stimulating effect of the former on plants 
and the attempts which have been made to make use of that fact 
in the employment of manganese salts as fertilizers. Moreover, 
our data form another link in the chain of evidence which show 
the stimulating effects of manganese sulphate on plants. 
It may not be amiss to add here, also, that to make these investi- 
gations more complete we have been making studies of the bacterial 
flora in the soils employed in the experiments above described. 
From these we have already obtained data of great interest, which 
seem to indicate that the soil flora is permanently modified by the 
treatment of the soil outlined above. The publication of these 
results is reserved for another paper. 
Sorts RESEARCH LABORATORY 
UNIVERSITY OF CALIFORNIA 
