Dec. 18, 1916 
Assimilation of Iron by Rice 
523 
in corresponding alkaline solutions when ferrous sulphate or ferric chlorid 
was the source of iron, but about equal percentages when ferric citrate 
or tartrate was the source of iron. With ferric chlorid, citrate, or 
tartrate an increase in the quantity of iron from 0.002 to 0.008 gm. of iron 
per liter in acid, neutral, or alkaline solution raised the percentage of iron 
in the plant. Increasing the ferrous sulphate in the acid solution did not 
increase the percentage of iron in the plants, while in the neutral solution 
it did have this effect. The percentages of nitrogen, phosphoric acid, 
lime, magnesia, and carbon-free ash in plants grown in six different 
solutions did not vary appreciably. The relative percentages of iron in 
the plants thus agreed with relative growths in showing that the amount 
of available iron in most solutions was the main factor controlling 
growth. 
In regard to the percentages of iron in the plants two anomalous fea¬ 
tures are apparent in the preceding tables: (1) The percentages of iron 
in plants supplied with ferrous sulphate were higher than in plants 
supplied with ferric citrate, and (2) in two cases plants which made no 
growth because of a lack of iron contained as high a percentage of iron as 
plants of good growth. 
Experiments 3 and 4 each afford a comparison of ferric citrate and 
ferrous sulphate in the three different nutrient solutions. In all cases 
0.002 gm. of iron per liter from ferric citrate produced a better growth of 
plants with a lower percentage of iron than did the same quantity of iron 
from ferrous sulphate. As tests 2, 3, 4, and 7 show, neither of these forms 
of iron, supplied at this rate, furnished sufficient iron for the maximum 
needs of the plant. Therefore the higher percentages of iron in the 
ferrous-sulphate plants could not have been due to excessive consumption. 
About the only explanation of the anomaly that occurs to the writers is 
that the ferrous-sulphate plants contained a certain amount of iron 
which was ineffective in the metabolism of the plant. In the solutions 
to which ferrous sulphate was added undoubtedly both ferrous and ferric 
iron existed in solution, while in the solutions with ferric citrate there was 
only ferric iron. It is possible that in the solutions with ferrous sulphate 
the plants absorbed both ferrous and ferric iron and that the ferrous iron 
was not so effective in the plant as the ferric iron. The ferrous-sulphate 
plants might therefore contain a certain amount of effective and non* 
effective iron. This explanation is somewhat doubtful, as it is not, to the 
knowledge of the writers, supported by similar well-established facts. 
The second irregularity is the high percentage of iron in plants 1 to 12, 
experiment 1, and plants 85 to 96, experiment 4, the former being grown 
without the addition of any iron to the solution, and the latter obtaining 
practically no iron from the alkaline solution, as proved by experiment 
10. . It is, of course, possible that the high percentages of iron were due 
to contamination, but this is thought not to be the cause. The plants 
made practically no growth and were so strongly chlorotic that they 
