70S Journal oj Agricultural Research vj.xxi.no. 10 
the total concentration of the solution, the relative proportions of the 
salt constituents, the total quantity of solution per plant, the age of 
the plants, and the condition of their aerial environment. From obser¬ 
vations made during the present study the last-named factor appears 
to have considerable influence in determining the rate of change of the 
hydrogen-ion concentration of the culture solutions here used. 
As previously stated, the hydrogen-ion concentrations of the culture 
solutions were determined at the end of the growth intervals between 
each two successive solution renewals throughout the entire growth 
period. In Table IV are presented the summarized data of these deter¬ 
minations in terms of P H values. Thus, in the table are given the initial 
P H values of the culture solutions, the highest and the lowest values 
obtained, and the average of all the values for each solution of the two 
series. Four days previous to harvesting the different cultures were 
compared with respect to yellowness of the leaves. The comparisons 
were made and values were obtained by means of the relative score 
method described by Free (4) for recording unmeasured plant charac¬ 
ters. To facilitate comparisons, the results of this score are given in 
Table IV in connection with the hydrogen-ion exponents, the lowest 
score value for any culture of the two series being considered as unity. 
Table IV.— P n values and score for yellowness of leaves of the culture solutions of the 
Toltingham series {A) and the ammonium-sulphate series (/-?) supplied with iron in the 
form of ferric phosphate 
Culture No. 
Tottingham series (A). 
Ammonium-sulphat 
:e series ( 
alucs. 
n). 
Score 
for 
yellow¬ 
ness. 
Ph values. 
Score 
for 
yellow¬ 
ness. 
I’ll V! 
Ini¬ 
tial. 
High¬ 
est. 
Low¬ 
est. 
Aver¬ 
age. 
Ini¬ 
tial. 
High¬ 
est. 
Low¬ 
est. 
Aver¬ 
age. 
TiRiCr. 
7. 0 
4.8 
6. 0 
5 -o 
5- 47 
0.0 
4.8 
5* i 
4. 4 
4. 68 
C 3. 
7. 6 
4. 9 
6. 2 
5- 2 
5-^7 
. 0 
4-8 
5-4 
4. 2 
4- 75 
C5... 
7- 7 
4. 8 
6. 2 
5 - 1 
5- 70 
. 0 
4. 9 
5- 9 
4. 2 
4- 85 
C7 . 
7- 7 
4- 8 
5-8 
S-o 
5-46 
2.0 
4. 9 
6. 0 
4. 4 
5. to 
R3C1. 
7- 7 
4.8 
6. 1 
5- 1 
5- 55 
. 0 
4. 0 
5-8 
4. 2 
4. 76 
C3 . 
i-3 
4.8 
6. 0 
5- 2 
5 -61 
. 0 
4.9 
6. 0 
4. 1 
4- 75 
Cs . 
7- 7 
4. 9 
6. 0 , 
5- 2 
5- 55 
1. 0 
4.9 
5- 0 
4. 1 
4 - 39 
R5C1. 
7. 8 
4.9 
5 - 9 
5- 0 
5 - 57 
1. 9 
4. 9 
5-6 
4. 1 
4. 62 
^3 .. 
7-7 
4.8 
6. 0 
5 - 2 
5. 60 
1. 0 
4. 9 
5 - 7 
4. 1 
4* 53 
R7C1. 
6. 6 
4. 9 
6. 0 
5 - 5 
5 - 7 i 
2. 0 
4. 9 
5 - 0 
4. 0 
4 - 59 
T3R1C1. 
4. 2 
4. 6 
5 - 9 
4.8 
5 - 33 
. 0 
4. 6 
5 -<» 
4. 2 
4. 70 
c 3 . 
4. 2 
4 - 7 
5-9 
4.8 
5-39 
• 0 
4.6 
5 - 2 
4. 4 
4. 69 
C5. 
4. 2 
4. 8 
5 - 9 
4. 9 
5 - 33 
. 0 
4.8 
5-8 
4. 6 
4. 89 
R3C1. 
4. 2 
4.8 
5 - 9 
5 *o 
5-39 
. 0 
4 - 7 
5- 2 
4. 1 
4 - 5 o 
C3. 
4. 2 
4. 8 
6. 0 
4.8 
5 - 40 
• 0 
4.8 
4. 9 
4. r 
4 - 4 7 
R5C1 . 
7. 6 
4 -S 
5 - 9 
5 - 1 
5 - 49 
. 0 
4.8 
5 - 7 
4. T 
4. 72 
T5R1C1 . 
4 - 3 
4. 6 
5-8 
4. 9 
5 - 24 
. 0 
4. 6 
5 - 7 
4. 4 
4. 84 
C3 . 
4.4 
4 - 7 
5 - 9 
4 - 7 
5 - 32 
. 0 
4. 6 
5 - 6 
4. 2 
4. 72 
R3C1 . 
4-3 
4. 6 
5 - 9 
4.8 
5 - 36 
. 0 
4. 6 
5 * 5 
4. 1 
4. 60 
TyRiCr.. . 
Shive’s — 
4.4 
4. 6 
5 - 9 
4.8 
5-32 
1. 8 
4. 6 
5 - 4 
4. 4 
4 - 70 
RsC2. 
1. 8 
4. 6 
5-6 
4. 6 
4. 96 
Tottingham’s — 
T3R1C4 . 
4. 2 
_ . 
4. 6 
5-4 
4. 6 
4. 94 
The data of Table IV show that the hydrogen-ion concentrations of 
the culture solutions of the Tottingham series were always considerably 
