5io 
Journal of Agricultural Research 
Vol. VII, No. xa 
proved by the pronounced chlorosis of the plants and by the results of 
experiment io. Here, as well as in experiment i, plants 85 to 96, which 
made practically no growth because of a lack of irori, contained a high 
percentage of iron in the dry substance. This point will be discussed 
later. 
Table IV. — Comparative weights of plants grown in acid , neutral , and alkaline solutions, 
with ferrous sulphate or ferric citrate as the source of iron 
Nutrient 
solution. 
Source of iron. 
Acid....... 
Ferrous sulphate. . 
.do. 
Do. 
Do. 
.do. 
Do. 
.do.. 
Do. 
Do. 
Ferric citrate. 
.do. 
Neutral. 
Do. 
Ferrous sulphate... 
.do. 
Do. 
.do. 
Do. 
.do. 
Do. 
Ferric citrate. 
Do. 
.do. 
Alkaline.... 
Do. 
Ferrous sulphate. . 
.do. 
Do....... 
.do... .*. 
Do....... 
.....do. 
Do. 
Ferric citrate. 
Do. 
.do. 
Quantity of iron 
per liter. 
Flasks No. 
ight of 
s and 
if 
u 
V • 
Average oven- 
dry weight of— 
fi 
< 5 j 3 
Green we 
stalk; 
leaves. 
Oven-dry 
of stall 
leaves. 
$8 
P 
6 
Stalks 
and 
leaves. 
Whole 
plant. 
Iron (Fes 
dry stal 
leaves. 
Gm. 
Gm. 
Gm. 
Gm. 
Gm. 
Gm. 
Per cU 
O. 
002 
1-6 
48.45 
6. 66 
1.47 
...... 
. 
- 4 * • • 
* 
002 
008 
7-12 
°13-18 
45-85 
91. 88 
6. 42 
12. 41 
x, 46 
3. 10 
6-54 
.8. 01 
.036 
• 
008 
002 
19-24 
23-30 
83.29 
6547 
10. 94 
8. 70 
2. 65 
1. 82 
11. 68 
14.56 
*032 
. 002 
. 002 
31-36 
37-42 
60. 07 
47 * 19 
8. 47 
6. 51 
1.83 
45 
8- 59 
10. 42 
. 026 
. 002 
. 008 
43-48 
49-54 
42 . 39 
r 00. 22 
5 - 92 
12.93 
i *35 
2.97 
6. 21 
7. 61 
. 017 
. 008 
. 002 
5 S- 6 o 
61-66 
100. 31 
62. 07 
58. 60 
45 - *8 
r 3 - 05 
8. 32 
7 . 85 
6. 17 
2. 90 
1.83 
1. 79 
1. 63 
12. 99 
r 5 * 93 
.023 
. 002 
. 002 
67-72 
73-78 
8. 09 
9. 90 
.015 
. 002 
. 008 
79-84 
85-90 
42. 13 
•93 
6. 22 
. 21 
1. 68 
. 11 
6. 20 
7. 86 
. 017 
. 008 
. 002 
91-96 
97-102 
103-108 
1. 07 
63. 28 
61. 85 
•23 
8.33 
8.29 
. 11 
2. 20 
. 22 
*33 
*049 
. 002 
2. 11 
8.31 
10.47 
. 012 
a Results calculated from five flasks. 
Experiment 5 (Ferrous sulphate in neutral solution with and without 
carbon black).—Data of growth in the different solutions seemed to point 
overwhelmingly to the iron supply as the factor controlling growth; 
nevertheless, it was possible that in some cases the precipitate in the 
solutions affected growth aside from any influence of the precipitate on 
the amount of soluble iron. After the addition of iron salts to the 
nutrient solutions a precipitate was formed which varied according to 
the source of the iron and the nutrient solution, but was greater as the 
amount of iron added became larger. In the preceding experiments a 
marked increase in growth was produced by increasing the iron from 
0.002 to 0.008 gm. per liter in the neutral solution. It was possible that 
the greater precipitate in the solution with 0.008 gm. of iron favored 
growth in removing by absorption traces of heavy metals or other sub¬ 
stances present in the distilled water. As carbon black and ferric hydroxid 
have been found to improve the quality of distilled water in this way, the 
following test was conducted. 
