33 
Treatment with iron salts, however, was signally effective in 
restoring the normal green color to the leaves. At first, 2 per cent 
solutions of ferrous sulphate were added to the soil in which chlorotic 
plants were growing without improving the condition of the plants 
at all. Crystals of ferrous sulphate were then put in the soil, either 
touching the roots or in their immediate vicinity. Three weeks 
after the application the treated plants had improved considerably 
in color, one month later the treated plants were practically a normal 
green and had increased considerably in growth. The untreated 
chlorotic plants which served as checks remained practically white 
and without growth. (PI. II, fig. 2.) 
Chlorotic plants were also treated by brushing the leaves with a 
2 per cent solution of ferrous sulphate, a 2 per cent solution of ferric 
chlorid, and a 2 per cent solution of sulphuric acid. The brushing 
was repeated four times, at intervals of 10 days. The plants treated 
with sulphuric acid showed no improvement, while those treated 
with the iron salts were considerably greener two weeks after the 
first brushing, and three weeks later were of a normal green. The 
facts that sulphuric acid was ineffective and that ferric chlorid and 
ferrous sulphate were equally effective in curing the chlorosis indi- 
cate that the action is to be attributed to the iron alone and not to 
the sulphate radical nor to the acidity of the salts. 
One plant, the leaves of which were almost waxy white, except 
for a few brown spots where decay was starting, was treated by 
dropping a crystal of ferrous sulphate in the heart. The center 
leaves were burnt out by the acidity of the salt, but the other leaves 
became green and a vigorous green shoot was sent out. 
The effectiveness of brushing with iron salts depends upon the 
solution penetrating the epidermis of the leaves. Leaves which were 
burnt by the strength of the solution became green much more 
rapidly than uninjured leaves. Leaves which were pricked previous 
to the brushing, so that the solution could penetrate readily, became 
green sooner than unpricked leaves. 
While the above treatments were signally effective in restoring the 
normal color and growth to plants, one treatment does not suffice for 
the life of the plant. Three or four months after the restoration of 
the green color, or chlorophyll, the new leaves commence to show 
chlorosis, and the whole plant gradually becomes chlorotic again. 
A renewed treatment with iron is again effective. 
To grow pineapples on strongly calcareous soils would necessitate 
repeatedly spraying the plants with ferrous sulphate, as applications 
of ferrous sulphate to the soil are unavailing. It is possible that on 
calcareous soils, containing from 2 to 5 per cent of calcium carbonate, 
an application of ferrous sulphate to the soil might be efficacious, as 
[Bull. 11] 
