MANGANESE CHLOROSIS OF PINEAPPLE. 35 
used for its potash, should be treated with acids when applied to 
manganese soils. Nitrate of soda should not be applied to manga- 
nese soils because of its injurious effects. The addition of humus- 
forming materials to the soils is emphasized in every system of 
agricultural practice. Such materials are of especial value to the 
soils of Hawaii which are of heavy clay character and have a tendency 
to puddle. It is recommended that stable manure or other humus- 
forming material be used if it can be applied at a a reasonable cost. 
Leguminous green manuring crops are very valuable. 7 
Pineapple plants should be sprayed with iron sulphate solution 
regardless of the kind of preparation given the manganese soils. 
No method of preparation of the highly manganiferous soils so far 
tested allows the plant to absorb sufficient iron and the iron spray 
should be applied as soon as any signs of yellowing appear. 
GENERAL SUMMARY AND CONCLUSIONS. 
A review is given of previous investigations on manganese. No 
conclusive proof is furnished in these of any stimulating action due 
primarily to manganese. The chlorotic effect found with higher 
concentrations of manganese has generally been attributed to an 
indefinite u toxic effect' of the manganese or to " manganese poison- 
ing.'' It was not proved in these previous investigations that 
manganese causes a deficiency of iron in the plant or that supplying 
iron will cure manganese "poisoning." 
The writer shows that the manganese of the highly manganiferous 
Hawaiian soils is present mainly in the dioxid form; that hydrogen- 
ion determinations indicate these soils to be acid; and that calcium 
carbonate is absent. 
A series of experiments were conducted with rice grown in nutrient 
solutions to determine the effect of manganous sulphate and manga- 
nese dioxid on growth where various amounts of iron were supplied 
to the nutrient solution from various sources. Preliminary experi- 
ments indicated that the effect of manganese depends largely on the 
amount of iron supplied by the solution. 
When the nutrient solution contained a normal amount of iron, 
manganous sulphate and manganese dioxid caused a strong chlorosis 
and a severe depression in growth. This chlorosis was overcome 
when the leaves were dipped in solutions of iron salts or the amount 
of iron in the nutrient solution was excessively increased. 
This manganese-induced chlorosis was thus shown to be due to a 
depression in the assimilation of iron or to a deficiency of iron in the 
plant. The previous results and conclusions of the writer concerning 
the manganiferous Hawaiian soils are thus confirmed. 
Manganese-induced chlorosis is altogether distinct from lime- 
induced chlorosis, due to calcium carbonate, since manganese-induced 
chlorosis can and usually does occur under acid conditions. Manga- 
nese and calcium carbonate can each produce an additive chlorotic 
effect in the presence of the other. 
No evidence was found to show that manganese exerts any stimu- 
lating effect on plant growth. With nutrient solutions containing 
7 The value of the different legumes is discussed in Hawaii Sta. Press Bui. 52, Comparative value of 
legumes as green manure. 
