418 BOTANICAL GAZETTE [JUNE 
gations dealing with the subject under discussion in which MnSO, 
has not been found, in relatively small quantities, to act as a 
stimulant is indeed very small. Obviously when very large con- 
centrations of MnSO, are employed it will be found toxic. As 
investigations of KELLEY above referred to have shown, a large 
variety of plants is affected more or less seriously by the manganese 
of soils which have shown a content of that material equivalent in 
some cases to more than g per cent of Mn,O, in the soil. However, 
such manganiferous soils are limited in extent and, undoubtedly 
even then, owe their unfavorable nature, in part, to the form of 
the manganese which they contain. This point appears to us so 
important as to render a comparison of past results on manganese 
investigations of little value when it is not considered. It would 
seem from our results in this series of experiments, and others of a 
similar nature which they help to confirm, that distinct increases in 
crop yields of certain plants may be induced by employing MnSO, 
in small quantities as a soil amendment. The manganese content of 
most ‘“‘normal’’” soils is very small, and therefore the dangers aris- 
ing from the presence of large amounts of manganese, as KELLEY 
has observed them on certain Hawaiian soils, are certainly very 
remote ones when considered in relation to these normal soils. 
Small additions of manganese should increase yields, therefore, 
without introducing dangers. We hope to report further results 
on this subject later. 
As was pointed out above, it has been suggested by some 
chemists, among the many other uses proposed for H,SO, when it 
is produced in enormous quantities from the SO, of the smelter 
fumes, that it could be employed in small quantities in the irriga- 
tion water, and, through the solution of mineral plant foods in the 
soil, be a considerable aid to the nutrition of plants directly, besides 
exerting perhaps a very marked influence indirectly on soil fertility 
as will be discussed later. In connection with soils containing 
black alkali, sulphuric acid would have an added value, if it were 
satisfactory in other ways, in that it would change the black to 
the white alkali more cheaply than gypsum does, and it could be 
applied more easily with irrigation water. Indeed, it is possible 
that in soils with a content of Na,CO,, not too large, the sulphuric 
10 Soils ordinarily cropped. 
