Jan. 26,1924 
Changes in Hydrogen-Ion Concentration 
215 
in reaction of the acid solutions. This is shown by the three final read¬ 
ings (before solutions were renewed or discarded) which give consistently 
higher acidities for the seedlings grown previously in defective nutrient 
solutions. The defectiveness of the previous nutrient solution evi¬ 
dently created in the seedlings some functional disturbance either 
general or with reference to their behavior toward the elements lacking. 
The most significant result obtained in this experiment, however, is 
that in the case of the older seedlings nitric acid had ceased to be affected 
by the action of the seedlings to a greater extent than the other acids. 
Its place was taken by phosphoric acid, as was shown by the three final 
readings in the series which had been grown in the complete nutrient 
solution. 
The initial acidity of phosphoric acid solution was reduced from P H 
3.6 to P H 5.2 in the final reading, a reduction which is strikingly greater 
than any obtained in the case of the other acid solutions. The differ¬ 
ences in the behavior of the various acids were thus brought out more 
distinctly. The preference of the seedling for the different acids was 
also shown to vary with the conditions and with the stage of growth. 
EFFECT OF AGE OF SEEDLINGS ON CHANGES IN REACTION IN ACID 
SOLUTIONS 
The effect of the age of seedlings on their behavior toward nitric and 
phosphoric acids, which was unexpectedly brought out by the previous 
results, was studied further. 
The usual procedure was followed. After the seedlings had been 
transferred to glasses and grown in tap water for three days, the roots 
were kept in contact with distilled water for two hours. The seedlings 
were then divided into two series. The seedlings of the first series were 
transferred to the acid solutions immediately. ‘ The seedlings of the 
second series were transferred to the acid solutions when 15 days old, 
after having been grown for 10 days in the nutrient solution diluted 
five times. The initial reaction of the acid solutions used was P H 3.6, 
which was more suitable than the initial reaction of P H 4, as the initial 
acidity was thereby increased 250 per cent and the changes produced 
were more pronounced. 
Table V.-— Effect of age of seedlings on changes produced in inorganic acid solutions* 
Reaction. 
Acid. 
Hydrochloric 
Nitric d . 
Sulphuric.... 
Phosphoric.. 
Hydrochloric 
Nitric. 
Sulphuric. . . 
Phosphoric. . 
Initial 
age of 
seed- After 
lings. 1 day. 
Days. 
Ph . 
5 4-05 
5 4* 40 
5 3-90 
5 4. 15 
i 5 
i5 
*5 
i 5 
After 
2 days. & 
After 
a days 
(2-day 
con¬ 
tact). 
P H‘ 
4. OO 
5 . IO 
4. IO 
Ph • 
3 - 6 
4- 3 
3- 6 
4*45 
3-9 
After 
6 days 
(4-day 
con¬ 
tact). 
Ph. 
After 
11 days 
(i-day 
con¬ 
tact). b 
After 
13 days 
(2-day 
con¬ 
tact)^ 
After 
17 days 
(a-day 
con¬ 
tact). 
After 
20 days 
(5-day 
con¬ 
tact). 
Pb. 
Pb. 
Ph • 
Ph. 
I 
I ' 
.i 
! 
4. SO 
4 - 75 
4.90 
5. 20 
3 - 90 
4. 00 
3 - 90 
4. 20 
4. 00 
4. 20 
4-30 
4 - 45 
4-35 
4. 60 
4 . 5 ° 
6. 15 
« Initial Ph, 3.6; number of seedlings, 20. 
i> Solution renewed after these readings were obtained. 
c Transferred to complete nutrient solution (1:5) for 2 days and then back to acid solutions. 
d Initial Ph, 3-5- 
