Aug. 15, 1921 
Effect of Ammonium Sulphate upon Plants 
709 
decreased during any growth interval. The culture solutions of the 
ammonium-sulphate series, on the other hand, usually increased some¬ 
what in hydrogen-ion concentrations. The average P n values of the 
culture solutions of this series do not vary greatly from the initial values. 
For most of the solutions these average values were slightly lower and 
a few were slightly higher than were the initial P n values of the solutions. 
To bring out more clearly the magnitude and the direction of the 
change in reaction of the culture solutions during the different intervals 
throughout the growth period, detailed hydrogen-ion concentration 
data for the culture solutions producing the highest, medium, and 
lowest yields in each of the series are given in Table V. From the data 
of this table and those of Table IV it can be definitely stated that the 
effect of the growing plants was always to decrease the hydrogen-ion 
concentration of the culture solutions of the Tottingham series and to 
increase the concentration of the hydrogen ions of the solutions of the 
ammonium-sulphate series, or, at least, to maintain the initial concen¬ 
trations of these ions during the first four weeks of the growth period. 
Table V.—Ph 'values of the culture solutions of the Tottingham series (A) and the 
ammonium-sulphate series ( B) producing highest , medium , and lowest yields with iron 
supplied in the form of ferric phosphate a 
Dates of solution renewals 
and growth intervals. 
Tottingham scries (A) producing— 
Highest 
yield 
(T7R1C1). 
Medium 
yield 
(t 3 ric S ). 
Lowest 
yield 
(TiR S C 3 ). 
1919. 
Aug. 22. 
4.6 
4.8 
4.8 
26... 
4.8 
4.9 
5-2 
0 2 9 . 
4.9 
5-o 
5-4 
5-0 
5*i 
5-4 
5 . 
5-i 
5-i 
5-3 
9 .'. 
5-4 
5-4 
5-5 
12. 
5-3 
5-3 
5-5 
16. 
5-7 
5-6 
5-9 
19. 
5-5 
5-6 
5-8 
2 3 . 
5-9 
5-9 
6.0 
27. 
5-6 
5-4 
6.0 
Average. 
5 - 3 2 
5-33 
5.60 
Ammonium-sulphate scries (B) 
producing— 
Highest 
yield 
(TiRiCs). 
4.9 
4.9 
5-0 
4.8 
4.6 
4.2 
4.6 
4.4 
4.2 
5-9 
5-9 
4-85 
Medium 
yield 
(T3R3C3). 
4.6 
4.8 
4.8 
4.6 
4.6 
4 - 7 
4.6 
4.6 
4.4 
5 - 2 
4.6 
4.69 
Lowest 
yield 
(T1R7C1). 
4.9 
4 - 5 
4.8 
4.4 
4.4 
4.1 
4.2 
4.1 
4.0 
5 - 9 
5-5 
4-59 
0 The first number in each column represents the initial P H value of the solution. 
The exact manner in which the hydrogen-ion concentrations of the 
nutrient solutions are altered by the growing plants has not yet been 
clearly demonstrated. Hoagland (8) has suggested that the change in 
reaction must be the result of the secretion of neutralizing substances by 
the plants, of chemical reaction with the material of the roots, or of the 
selective absorption of specific ions. As a result of extensive studies of 
absorption of ions by plants, Pantanelli (13) ascribes the change in re¬ 
reaction of the nutrient media mainly to the differential absorption of 
the ions by the living plant roots. 
