Dec. 18,1916 
Assimilation of Iron by Rice 
505 
In analyzing the plants for iron the substance was ashed over a low 
flame without the addition of calcium acetate and iron determined colori- 
metrically by the method of Stokes and Cain (14). In attempting to 
estimate the soluble iron in the nutrient solutions, the solutions, were 
filtered, the filtrate concentrated when necessary, and iron determined 
colorimetrically by the above method. The ordinary colorimetric method 
with potassium sulphocyanate (KSCN) was used in some of the pre¬ 
liminary work, but all the determinations reported were made by the 
method of Stokes and Cain unless otherwise specified. Blanks were run 
for iron with the acid and materials employed. 
PRELIMINARY EXPERIMENTS 
Following are the data of three preliminary experiments conducted 
before a uniform method was adopted: 
Experiment i (Source of iron: Ferrous sulphate. Plants grown in 
double flasks).—It was at first thought it would be advantageous to 
grow the plants with their roots equally divided between two flasks, one 
flask to contain the acid solution and the other the neutral. By adding 
iron only to the acid solution in one lot and only to the neutral solution 
in another lot it was thought that decisive results would be obtained 
on the effect of the reaction of the solution on the assimilation of iron, 
as the only difference between the two lots would be in the solution in 
which iron occurred. The results, however, did not bear out the assump¬ 
tion. 
Two plants were grown in each twin flask (A and B). Four flasks were 
taken as a unit and the units triplicated for each treatment. All solu¬ 
tions containing iron contained the same quantity, but in this experiment 
the quantity of iron was not kept constant during the 40 days of growth, 
as it was thought that at first so much iron was added as to obscure the 
effect of the reaction on assimilation. During the first 10 days 0.008 gm. 
of iron per liter was used, during the second 10 days 0.004 g m - of iron, 
and during the last 20 days 0.002 gm. of iron. In Table I are given the 
weights of the plants grown in the different solutions, together with the 
percentages of nitrogen and iron in the dry substance. 
The color of the plants during growth was as follows: At 10 days 
plants 1 to 12 were strongly chlorotic, plants 25 to 36 were chlorotic, 
plants 13 to 24 and 49 to 60 were green, and plants 37 to 48 were dark 
green; from the twentieth to the fortieth day plants 1 to 12 were strongly 
chlorotic and all others were about the same normal green. 
From the weights of the stalks and leaves it appears that with the 
quantities of iron used the reaction of the solution had little effect on 
the assimilation of iron. It also seems that there is no advantage in 
growing the plants with their roots divided between two flasks, as one- 
half the roots are not able to absorb sufficient iron for the full needs of 
