24 BULLETIN 52, HAWAII EXPERIMENT STATION. 
increase in growth due to its removal of some of the excessive iron 
present. 
Manganese dioxid and calcium carbonate combined with 5, 10, 
20, and 40 milligrams per liter of iron caused a strong chlorosis and 
a severe depression in growth. The chlorosis was overcome when the 
leaves were dipped in iron or when the iron supply was increased to 
80 milligrams. 
Experiments III and VI may be considered together since the 
plants were grown in each for the same length of time with the same 
solutions and each had approximately the same check. This has 
been done in Figure 4. A study of Tables 3 and 6 and Figure 4 
indicates that calcium carbonate and manganese dioxid have the 
same effects. Although the above-mentioned results were obtained 
when calcium carbonate and manganese dioxid were used singly in 
excessive amounts, the chlorosis was very greatly increased when 
the two were used in combination. Manganese dioxid and calcium 
carbonate each appears to possess its own peculiar chlorotic effect 
and to exert an additive chlorotic effect in the presence of the other. 
Discussion of Results. 
The results obtained show that manganous sulphate and manga- 
nese dioxid cause a strong chlorosis and a severe depression in the 
growth of the plant. This chlorosis is overcome when the leaves are 
dipped in iron solutions or when the amount of iron in the nutrient 
solution is excessively increased. Manganese thus apparently 
causes a depression in the assimilation of iron by the plant or a 
deficiency of iron in the plant. This confirms the results with pine- 
apples previously obtained by the writer. Many investigators have 
found that manganese, especially in large amounts, causes chlorosis, 
but none has offered proof to show that manganese-induced chlorosis 
is due to a depression in the assimilation of iron or to a deficiency of 
iron in the plant. 
Manganese-induced chlorosis occurs in acid solution and is alto- 
gether distinct from lime-induced chlorosis which is caused by 
calcium carbonate. In the latter instance the availability of the iron 
is reduced by the alkalinity of the solution. Manganese and calcium 
carbonate can each exert an additive chlorotic effect in the presence 
of the other. 
Since chlorosis is produced by manganese in acid solutions with no 
excess of lime, it is proved conclusively that chlorosis in general is 
not due to the alkalinity of the solutions or to excess of lime, but 
simply to deficiency in iron. 
Manganese is commonly referred to as a plant stimulant. In 
these experiments manganese has been found to cause increased 
growth only when the solution contained a large excess of iron, some 
of which the manganese dioxid removed. 
AN EXPLANATION OF THE PHYSIOLOGICAL EFFECTS OF MANGANESE 
ON PLANTS. 
Pugliese (37) and Tottingham and Beck (44) have suspected an 
antagonism between manganese and iron. In the writer's opinion, 
however, the physiological effect of manganese, at least the effect of 
the manganiferous soils, can be explained on purety chemical grounds. 
Hildebrand (22) gives a titration curve for ferrous sulphate in which 
