706 
Journal of Agricultural Research 
Vol. XXI, No. io 
EXPERIMENT I. FERRIC PHOSPHATE AS THE SOURCE OF IRON IN THE 
SOLUTIONS OF SERIES A AND OF SERIES B 
The importance of the proper amounts and forms of iron to be used 
with a given nutrient solution in order that the plants may be adequately 
supplied with this element for normal growth can scarcely be over¬ 
estimated. As has been shown by Gile and Carrero (6) and pointed out 
also by Hoagland ( io ), the presence in culture solutions of sufficient 
available iron for the development of green plants depends largely upon 
the form and amount of the iron salt used, upon the reaction and con¬ 
centration of the nutrient solution in which it is used, and upon the 
time of standing. It should be added also that the different species 
vary considerably in their requirements for this element and in their 
ability to obtain it from nutrient solutions, as has been clearly brought 
out in preliminary experiments in connection with this study. 
Table III .—Relative dry-weight yields of wheat tops and roots from Tottingham's series 
(A) and from the ammonium-sulphate series (B) with equivalent amounts of iron sup¬ 
plied to each culture in the form of ferric phosphate or ferrous sulphate « 
Culture No. 
Experiment I, source of iron FePO*. 
Series A. 
Tops. Roots. 
Series B. 
Tops. Roots. 
Experiment II, source of iron FeSO*. 
Series A. 
Tops. Roots. 
Series B. 
Tops. Roots. 
T1R1C1. 
Gm. 
1.00 
c 3 . 
(• 7352) 
1-35 
1-32 
• 72 
.92 
•94 
• 79 
.82 
C 5 . 
C7. 
R3C1. 
C 3 . 
C5. 
R5C1. 
C3. 
•65 
. 78 
R7C1. 
T3R1C1. 
1.44 
C3. 
1.40 
c 5 . 
T. 20 
R3C1. 
1.43 
c 3 . 
1.20 
RsCi. 
1.18 
T5R1C1. 
1.36 
c 3 . 
f:ii 
R3C1. 
T7R1C1. 
1.69 
Shive’s R5C2. 
I. *71 
Tottingliam’s T3R1C4 
1.65 
Gm. 
Gm. 
Gm. 
1.00 
1.00 
1.00 
(• 1975 ) 
1.67 
( iM ,6) 
(. 2609) 
2.41 
1.02 
2.05 
2.30 
.91 
I. IO 
1-53 
1.11 
1. 26 
1.11 
1.27 
.96 
i:« 
1.42 
1.61 
.86 
.98 
.92 
.96 
1.12 
1.23 
1. 22 
.96 
1.46 
1.47 
1.40 
1.80 
1.87 
1.68 
2.22 
1.77 
1.18 
1.42 
1.42 
1.50 
1.72 
1.16 
1.49 
i -57 
l.$2 
i:& 
1.27 
1.15 
1.72 
I -13 
1. 04 
1.'87 
2.09 
2-33 
1.42 
I -13 
1.42 
i -34 
Cm. 
1. oo 
(1.0.189) 
8.17 
2. 61 
1-39 
2. 04 
8.26 
2.47 
2 - 55 
2.83 
2.42 
1. 8 S 
2.97 
2.99 
3.15 
2.17 
3.24 
2-37 
1. 81 
2.99 
2.96 
2-39 
2.49 
Gm. 
1.00 
(• 2452) 
2.98 
2.65 
1. 79 
1-35 
2.93 
3.88 
2.12 
2.89 
1.63 
1.47 
3.26 
3.02 
1.63 
2. 20 
2. 77 
1.92 
2.00 
2.00 
2.85 
1.84 
3-30 
Gm. 
1.00 
(.9016) 
•95 
.96 
• 74 
• 74 
.81 
•57 
•6.S 
. 6r 
.69 
1.16 
1.09 
•84 
1.01 
•76 
i.*io 
Gm. 
1.00 
(• 1724) 
1.01 
1.04 
. 90 
.84 
•87 
•58 
•65 
•58 
• 70 
1.16 
1.10 
•54 
• 96 
•76 
•94 
• 79 
•94 
•97 
• 74 
•95 
a Data from the six high-yielding cultures are given in bold-face type 
Iron salts are, of course, more soluble in solutions of higher hydrogen- 
ion concentration than they are in solutions with lower concentrations 
of the hydrogen ions; but as Hoagland (ro) has pointed out, certain 
forms of iron may be completely precipitated in a relatively short time 
when the total phosphate content of the solution is high. It appears, 
however, that the insoluble ferric phosphate used in the nutrient solu¬ 
tions here considered may be made available to the plants under certain 
conditions, as will be brought out by a study of the data presented in 
connection with these experiments. 
