522 
Journal of Agricultural Research voi.v1x.No.12 
Table XIV .—Relative growths of rice plants with 0.002 and 0.008 gm. of iron per liter 
in the different solutions 
Source of iron in nutrient solution. 
Growth 0 with 0.008 gm. 
ot iron per liter in— 
Table 
from 
which 
data 
were 
calcu¬ 
lated. 
Acid 
solu¬ 
tion. 
Neu¬ 
tral 
solu¬ 
tion. 
Alka¬ 
line 
solu¬ 
tion. 
Ferrous sulphate. 
141 
179 
212 
209 
197 
141 
127 
100 
13s 
118 
II 
IV 
V 
VI 
XI 
IX 
VII 
VIII 
Do... 
4 . 
Do.. . . 
Ferric chlorid. . 
131 
140 
Do . 
Dialyzed iron .■ . /... 
Ferric citrate. 
162 
98 
90 
130 
Ferric tartrate . . 
a Growth with 0.002 gm. of iron per liter=100. 
In most cases an increase in the amount of iron added to the solution 
produced a marked increase in growth. With ferric tartrate in the acid 
solution an increase in iron produced no increase in growth, as apparently 
the smaller quantity of iron was adequate. In the alkaline solution 
with ferric citrate and with ferrous sulphate there were, respectively, 
no increase and a striking depression in growth, following an increase 
in the amount of iron added to the solution. Increasing the ferric 
citrate in this solution apparently did not increase the soluble iron and 
increasing the ferrous sulphate must have decreased it, as the smaller 
amounts of iron were also inadequate in these solutions. 
From the growth of the plants it appears that ferrous sulphate, ferric 
citrate, or ferric tartrate used in proper quantities afforded sufficient 
iron in acid or neutral solutions. With the two quantities of iron used 
ferric chlorid was inferior as a source of iron, and dialyzed iron was utterly 
inadequate. Ferric tartrate was the only form of iron tried which 
appeared to afford sufficient iron in the solution alkaline with calcium 
carbonate. 
The addition of carbon black to the neutral nutrient solution with 
0.002 gm. of iron per liter very slightly depressed growth, but carbon 
black in the solution with 0.008 gm. of iron did not affect the yield. 
Treating the distilled water with carbon and filtering previous to its use 
in the nutrient solution increased growth considerably over that in the 
ordinary nutrient solution. 
Doubling the phosphates in the neutral nutrient solution did not 
measurably affect growth when either ferric chlorid or citrate was used 
as the source of iron. 
In all the cultural tests, plants grown in acid solutions contained more 
iron than those grown in corresponding neutral or alkaline solutions. 
Plants grown in neutral solutions contained more iron than those grown 
