512 
Journal of Agricultural Research 
Vol. VII, No. 12 
solution from adsorbing to any extent these injurious substances. The 
slight depression in growth produced by carbon in the solution with 0.002 
gm. of iron may well be due to slightly diminishing the amount of soluble 
iron in the solution by adsorption. 
It thus seems possible that the larger flocculent iron precipitate which 
existed in the solution with 0.008 gm. of iron per liter may have increased 
growth to some extent by improving the distilled water; but only a small 
part of the greater growth produced by increasing the iron from 0.002 to 
0.008 gm. can be attributed to that cause. 
Experiment 6 (Source of iron in acid, neutral, and alkaline solutions: 
Ferric chlorid).—The results with ferrous sulphate as the source of iron 
may well be complicated by the fact that both ferrous and ferric iron 
doubtless existed in the solution unless the ferrous iron was oxidized by 
the plants' roots (13). In the very dilute solutions it was, of course, 
impossible to tell how much of each kind of iron was present. In the 
following experiment with ferric chlorid as the source of iron naturally 
ferric iron only was present. 
Ferric chlorid was added to the acid, neutral, and alkaline solutions so 
as to furnish 0.002 and 0.008 gm. of iron per liter. Two seedlings were 
grown in each flask, six flasks were taken as a unit, and the units tripli¬ 
cated for each treatment. The growth of plants and percentages of iron 
in the dry substance are given in Table VI. 
Table VI. — Comparative weights of rice plants grown in acid, neutral, and alkaline solu¬ 
tions, with ferric chlorid as the source of iron 
Nutrient solution. 
Quantity 
of iron 
per liter. 
Flasks No. 
Green 
weight 
of stalks 
and 
leaves. 
Oven- 
dry 
weight 
of stalks 
and 
leaves. 
Oven- 
dry 
weight 
of 
roots. 
Average 
oven-dry 
weight of— 
Stalks 
and 
leaves. 
Whole 
plant. 
Iron 
(FeaOa) 
in dry 
stalks 
and 
leaves. 
Gm. 
Gm. 
Gm. 
Gm. 
Gm. 
Gm. 
Per ct. 
Acid 
Do 
Neutral 
Do..- 
Alkaline 
Do 
o. 002 
. 008 
. 002 
. 008 
. 002 
. 008 
I- 6 
7- 12 
13- 18 
19' 24 
25 ' 30 
3 1 ' 36 
37 ' 42 
43 - 48 
49 ' 54 
55' 60 
61- 66 
67- 72 
73 ' 78 
79 - 84 
85- 90 
91- 96 
97-102 
103-108 
26. 50 
32.37 
24. 96 
37 - 67 
39-43 
34.62 
29. 72 
28. 22 
29.56 
38. 12 
41. 76 
40. 70 
6.96 
6.97 
6- 33 
10. 03 
9- 26 
7.81 
3 - 89 
4 - 59 
3 - 46 
5 - 32 
5 - 49 
4.78 
4 . l6 
3- 81 
3 -83 
5 - 17 
5. 82 
S- 65 
I. 09 
I. IO 
•97 
i. 5 i 
1. 36 
1. 22 
o. 75 
.87 
.68 
■97 
1. 10 
•94 
.83 
. 80 
.85 
1.03 
1. 21 
1. 16 
*32 
•33 
• 3 i 
.42 
•37 
•33 
3-98 
4-75 
0. 025 
5. 20 
6. 20 
. 026 
3-93 
4.76 
. 022 
5 - SS 
6. 68 
. 026 
I- 05 
r * 37 
. 022 
I. 36 
73 
. 023 
