Dec. xS, 19x6 
Assimilation of Iron by Rice 
509 
Increasing the quantity of iron from 0,002 to 0.008 gm. per liter greatly 
increased the growth in both the acid and neutral solutions. 
Analyses showed' that plahts grown in the different solutions did not 
differ appreciably in their percentages of nitrogen, phosphoric acid, lime, 
magnesia, or carbon-free ash, but did differ materially in the quantity 
of iron they contained. Plants grown in the acid solutions contained 
about 50 per cent more iron than plants grown in corresponding neutral 
or alkaline solutions. 
In the course of this and other work it has been found that the color of 
the leaves is a pretty good indication of whether or not the plant is ob¬ 
taining sufficient iron, although a lack of green is often attributable to 
other causes than a lack of iron. During growth, plants in the acid 
solution were the darkest green, in accordance with the percentages of 
iron found in the plants. 
Used at the rate of 0.002 gm. of iron per liter ferric citrate was plainly 
a better source of iron than ferrous sulphate, especially in neutral and 
alkaline solutions. 
That the growth in the different solutions was largely controlled by 
the supply of available iron seems proved by the color and analyses of 
the plants, and by the increased growth following an increase in quantity 
or change in the kind of iron added to the solutions. 
FINAL EXPERIMENTS 
Experiment 4 (Sources of iron in acid, neutral, and alkaline solutions: 
Ferrous sulphate and ferric citrate).—In this experiment 0.002 and 0.008 
gm. of iron per liter from ferrous sulphate and 0.002 gm. of iron from 
ferric citrate were tested in the three different nutrient solutions. Two 
plants were grown in each flask and six flasks were taken as a unit, the 
units being duplicated for each treatment. The data of growth and the 
percentages of iron in the dry substance of the stalks and leaves are given 
in Table IV. 
The color of the plants during growth was as follows: At 10 days plants 
1 to 24 and 49 to 60 ^Vere a good green, all others were a yellowish green 
except plants 85 to 96, which were strongly chlorotic; at 20 days plants 
1 to 24 and 49 to 72 were a good green, plants 25 to 48, 97 to 108, 73 to 
84, and 97 to 108 were a slightly poorer color, and plants 85 to 96 were 
almost white. 
The results of this experiment confirm those of the preliminary experi¬ 
ments in respect to (1) the superiority of ferric citrate to ferrous sulphate 
as a source of iron, (2) the relative growths in acid and neutral solutions 
with the two quantities of iron, and (3) the markedly higher percentages 
of iron in plants grown in the acid solutions. The new fact established 
was that increasing the iron from 0.002 to 0.008 gm. per liter in the alka¬ 
line solution depressed the growth of plants to a surprising degree. That 
the lack of growth in this solution was due to a lack of available iron is 
