416 BOTANICAL GAZETTE [JUNE 
a corrosive effect on plants, and that a too rapid displacement of 
bases in the soil and their subsequent leaching tends to cause soil 
acidity. 
It is to be regretted that EHRENBERG’S researches were carried 
out from the point of view merely of establishing the feasibility of 
employing vegetation cylinders containing zinc, and therefore we 
have nothing to guide us to the extent of the solution of zinc and 
the toxic limit thereof. It appears to us, further, that it is begging 
the question to assert that the toxic effect of zinc on soil organisms 
is of benefit to plants for the reason mentioned, because we have 
no definite data concerning the effects of zinc on soil bacteria or 
other soil organisms, and certainly not evidence enough, so far, to 
point to wide differences between the effects of zinc on the higher 
plants and soil bacteria. From the data in table II, at any rate, 
it would appear that plants will tolerate and will not be affected by 
even very considerable quantities of zinc. In connection with this 
series of experiments in particular, it is desirable to have more 
experimental data, which we are attempting to secure in further 
experiments now under way. 
The numerous and conflicting results obtained by different 
investigators in the study of the physiological effects of manganese 
salts on plants made it desirable to work further with these inter- 
esting compounds, and an experiment was arranged, therefore, in 
which this problem could be studied. The arrangement of the 
experiment with the results obtained are given in table III. 
TABLE III 
Errects oF MNnSO, oN PLANTS 
DRY WEIGHT OF VETCH _ Day WEIGHT oF 
MnSO, ppm. ‘ces iE 
Roots gm. Tops gm. Tops gm. 
Oo ae 4-5 12.0 18.5 
WO. Por Ce 4.0 9-5 16.2 
BO 4.5 8 lo 20.0 
BO pi Sah ie de ee VS 6.0 15.0 yes We 
ROSS ey tak Ce ie 4.0 18.0 25.1 
8 Pe Ps a oa aera een Poe loa 5.0 sy a3.2 
OG ie os hs a vt 5.5 19.5 26.0 
GO ee i a a a8 10.0 g2.5 
