274 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9 
Comparison of Different pH Values with Continuously 
Renewed Solutions 
On the basis of the results of the preceding experiment, o.i the usual 
concentration of Livingston and Tottingham's solution R8C1 was chosen 
for this test. Two cultures were arranged at each of three degrees of 
acidity as follows: 5.3 pH, 6.4 pH, 7.5 pH. The pH values were adjusted 
by adding KOH with use of the appropriate indicators used by Clark and 
Lubs. For this purpose, 0.9 cc. of NI2 KOH per liter of diluted nutrient 
solution was required for the highest pH value and 0.5 cc. for the inter- 
mediate one. Seedlings reared in flowing tap water were grown in these 
solutions of different pH values, continuously renew^ed at approximately 
the rate of 2 liters per jar per 24 hours. The growth period extended from 
May 20 to June 7. During this time the atmometer measurements taken 
adjacent to the cultures were as follows: 
Mean daily evaporation from standard spherical white, atmometer, 19. i cc. 
Mean daily evaporation from standard spherical black atmometer, 25,1 cc. 
Ratio of black to white instrument, 1.3 1. 
The data of yields appear in table 4. 
Table 4 
pH Value of 
Solution 
Average Length 
Average Dry Weight 
Tops 
Roots 
Tops 
Roots 
Mm. 
Mm. 
Mg. 
Mg. 
5-3 
6.4 
7-5 

182 (18)* 
258 (45) 
295 (58) 
106 (6) 
245 (33) 
300 (75) 
229 (9) 
367 (76) 
512 (218) 
108 (5) 
198 (17) 
230 (35) 
Second Test 
6.4 
7.5 
178 (3) 
188 (0) 
175 (25) 
213 (13) 
170 (9) 
141 (5) 
96 (3) 
75 (3) 
* Average departure from mean. 
At the end of the test the plants grown at pH 5.3 had short root systems, 
especially as regards secondary roots, and the leaf tips were withered. 
Both of these conditions are characteristic of acid injury. The growth 
response at the two higher pH values was irregular. Both groups of plants 
at pH 6.4 were superior to those grown at pH 5.3, but one culture at the 
former pH value was much superior to the other in appearance of roots and 
tops. At pH 7.5 one culture was but little superior to the poorer one at pH 
6.4, while the other gave profuse elongation of roots and development of 
tops. 
In view of these discrepancies, the comparison of pH 6.4 and 7.5 was 
repeated. For this purpose seedlings were available which had been reared 
