28 BULLETIN 52, HAWAII EXPERIMENT STATION. 
with iron sulphate solution, and all of the plants have made normal 
growth. 
Experiment III. — To show that it is the iron that is effective in 
restoring the normal green 'color and health to the plant, and to 
ascertain the effects of some fertilizing elements in combination with 
iron, the leaves of very yellow plants were brushed four times at 
intervals of a week each with various solutions and the condition of 
the plants was observed one, two, and three months later. 
It was observed that the plants which were brushed with a 2 per 
cent solution of iron sulphate gave results similar to those obtained 
in Experiment II, and that other plants were not benefited by the 
application of a pint of the solution to the soil near the roots. " The 
application to the roots of several ounces of iron sulphate crystals 
was of some benefit, but not nearly so much so as was the applica- 
tion to the leaves of the solution containing a small amount of iron 
sulphate. No change was noted in plants which were brushed with 
a 4 per cent solution of sulphuric acid, and very slight change oc- 
curred when dilute acid was applied to the soil in quantities of one- 
half pint and 1 pint per plant. Plants which were brushed with a 
2 per cent solution of ferric chlorid (iron chlorid) appeared better 
than did those which were brushed with iron sulphate, having a 
fine, -dark green color. The chlorid, however, has a tendency to 
burn the plants. The application of ferric chlorid to the soil was of 
very little benefit to the plants. The application of a solution of 
soluble ferric phosphate to the leaves of the pineapple plant was of 
some benefit, but the application of solutions and crystals to the 
soil near the roots was of little value. Ferric ammonium sulphate 
when applied to the leaves in solution and as crystals to the roots 
was beneficial, but solutions applied to the roots had no effect. 
In order to secure, if possible, beneficial action similar to that se- 
cured from the use of stable manure, due to solvent action of organic 
acids, 2 per cent solutions of citric, oxalic, and acetic acids were ap- 
plied to the soil near the roots of the plants but without noticeable 
results. It would seem that the temporary beneficial action of the 
manure is to be ascribed to the growing of the plant in the manure 
rather than in the manganese soil, as it was necessary to apply large 
amounts of the manure to the rows. An* injection of iron sulphate 
near the base of yellow plants was of little value. 
Sulphuric acid added in quantities of 1 per cent to the iron sul- 
phate solution gave results slightly more beneficial than when iron 
sulphate alone was used but showed an increased tendency toward 
burning. A solution containing 4 per cent of ammonium sulphate 
in addition to the iron sulphate gave beneficial results. Spraying 
with solutions containing ammonium sulphate in addition to the iron 
sulphate seems to be of value in that it supplies ammonium salts 
which are known to be of benefit to pineapples. 
From these trials it is evident that the restoration of the normal 
green color and healthy appearance of the plants is due to the iron 
which is contained in the iron sulphate solution applied to the leaves. 
That it is not due to acidity of the salts or the sulphate radical is 
shown by the unsuccessful results when solutions of sulphuric acid 
were applied to the leaves. 
Experiment IV. — Previous experiments having indicated that the 
application to the leaves of solutions of iron sulphate alone, of iron 
