362 Jones and Skive.—Influence of Ammonium Sulphate 
representing the yields of tops and the lower set the root yields. The dry- 
weight values as ordinates are here plotted against the amounts of iron 
in milligrams per litre of solution as abscissas. 
Table II. 
Hydrogen-ion concentrations and dry-zveight yields of soybean tops and roots 
grown in two types of nutrient solutions supplied with varying amounts 
of iron in the form of ferric phosphate and ferrous sulphate . 
Series C. 
Source 
Amounts 
( Tottingham solution 
yf 
iron. 
of iron 
mg. per 
litre. 
Dry weights. 
Tops. 
Roots. 
Mg. 
Grm. 
Grm. 
0-00 
1-6053 
0.2795 
0-01 
1.7109 
0-3561 
O-IO 
2-4170 
0 * 47 1 5 
0.25 
2-2737 
o -3734 
0.50 
2-6455 
0-4768 
FeP 0 4 
o -75 
2-6365 
0-4188 
1.00 
3 - 594 2 
0.6101 
1.50 
4.0236 
0-6963 
2.00 
4.3687 
0*7880 
3.00 
4-3458 
0-6555 
5 *°° 
3 - 79 6 5 
o- 66 n 
0-00 
1-6053 
0.2795 
O-OI 
2.2793 
0-4510 
O-IO 
4-1461 
°- 75 : 7 
0.25 
4.3252 
0-7253 
0.50 
4.2039 
0.6045 
FeS 0 4 
o -75 
3 - 474 1 
0.4942 
I -oo 
3-9358 
0-5178 
1.50 
3-9546 
0.5487 
2-00 
3.7229 
0-4334 
3.°° 
3.6916 
0.4878 
5.00 
3-3245 
0.4025 
Series D. . 
(.Modified Tottingham solution 
T \.R\CP). 
H-ion 
Dry weights. 
Pi-ion 
concen¬ 
trations. 
Tops. 
Roots. 
concen¬ 
trations , 
pH 1 
Grm. 
Grm. 
pH 
5-75 
3.7769 
0.4920 
4-53 
<v 8 o 
4.2117 
0-5428 
4*53 
5-87 
4-5662 
0-6320 
4-44 
5-89 
4 - 39 01 
o- 7 ii 3 
4.64 
5-94 
4-3 7 1 5 
°- 7 1 57 
4.67 
5-98 
4-0922 
0.7309 
4.67 
6.03 
4 , 4 I 93 
0.6973 
4-73 
6-09 
4-2285 
o- 7 1 57 
4-62 
6.13 
4-5789 
0.7041 
4-75 
6-19 
4.4721 
0.7079 
4-59 
6-03 
4.1796 
0.6328 
4-63 
5’75 
3-7769 
0.4920 
4-53 
5-85 
4.6748 
0-7386 
4-53 
6-24 
4.8910 
0-6485 
4.49 
6.23 
3.9627 
0.4429 
4-49 
6-20 
3 - 1 44 ° 
0-3168 
4.50 
6.15 
2.7560 
0.3619 
4-56 
6-14 
2.8513 
0.3485 
4-57 
6-13 
2-1728 
0-2753 
4'57 
6.08 
2-1432 
0.2725 
4-54 
6.07 
i-8180 
0-2417 
4.58 
6 -oi 
1-9621 
°- 3 I 49 
4'57 
As indicated by the graphs of Fig. 1 the varying amounts of iron 
in the form of ferric phosphate have a very great influence on the increase 
of the dry-weight values of the tops and roots in the Tottingham series C. 
The graphs strikingly show that a maximum growth can be obtained in the 
ammonium-sulphate series D with a very small amount of iron in this form, 
and that increasing the amount does not increase the yield. In the case of 
the Tottingham series C the yields of the cultures do not begin to approach 
the yields of the ammonium-sulphate series D until 1 milligrams or more 
of iron are employed. From the results of this experiment it may be 
stated in general that the presence of ammonium sulphate in a solution, either 
through its influence on the hydrogen-ion concentration or the possible 
1 These values represent the averages of all the determinations made for each solution at the 
end of the growth intervals throughout the experiment period. The initial pH value of all the solu¬ 
tions in each series was approximately 4-8. 
