jan. i 9l 1924 Photoperiodism and Hydrogen-Ion Concentration 137 
To study further the effect of the light period on acidity, plantings 
were made in six metal buckets of 12-quart capacity on June 30, and the 
seedlings were above ground on July 3. One series of three buckets 
remained out of doors throughout the test, while a second series of three 
buckets was permanently transferred from the full length of day to a 
io-hour day on August 5. The latter series began flowering August 29. 
The former series began flowering September 15, although flower buds 
could be seen a week earlier. The results of the observations are shown in 
Table V and figure 10. These studies were only begun shortly before the 
plants passed into the flowering condition as a result of the natural 
decrease in length of day, for it is known that a minimum period of at least 
3 weeks is required for the unfolding of the blossom after the plant comes 
under the influence of a favorable day length. It will be seen that under 
the natural length of day there is a decided decrease in acidity for about 
one week ending August 19, immediately followed by a sharp increase 
which continues progressively till after flowering has begun. Abrupt 
shortening of the daily light period to 10 hours had somewhat reduced 
the hydrogen-ion concentration at the end of 48 hours, but the full 
effect of the change did not come about till the end of 5 or 6 days. There¬ 
after there was a sharp progressive increase in acidity just as under the 
natural decrease in length of day. The effect of the io-hour day, however, 
was to accentuate and to hasten these changes in acidity. Biloxi soy 
beans thus closely resemble cosmos in acidity relations except that the 
relatively reduced stem elongation characteristic of the soy beans in the 
vegetative condition is associated with a decidedly lower maximum 
acidity of the apical structures than is attained in cosmos, in which 
marked elongation of the axis takes place. 
Table V. —Showing the Ph value of the cell sap of the young , topmost leaves of Biloxi 
soy beans grown in buckets when exposed to the natural change in length of day in late 
summer and fall and when abruptly transferred from these conditions of illumination 
to a io~hour day . 
Time at which sample was taken. 
Date. 
Hour. 
Aug. 7.. 
Aug. 9. 
Aug. 11. 
Aug. 13. 
Aug. 16. 
Aug. 19. 
Aug. 24. 
Aug. 31. 
Sept. 1.. 
Sept. 7. 
Sept. 16 
Sept. 21 
9.30 a. m.. 
9.20 a. m.. 
9.30 a. m.. 
9.10 a. m.. 
9.20 a. m.. 
9.40 a. m.. 
11.15 a. m. 
10.05 a - m ‘ 
12.15 P- m 
11.25 a. m. 
9.45 a. m.. 
11 a. m_ 
Plants 
Plants 
exposed to 
natural length 
of day 
throughout 
the test. 
Ph value. 
permanently 
transferred 
from the 
natural length 
of day to a io- 
hour day on 
Aug. 5. 
Ph value. 
6.28! 
6. 44 
6. 31 
6. 52 
6. 41 
6 * 95 
6. 56 
7. 00 
6.36 
6. 60 
6. 70 
6. 51 
6.33 
6. 32 
6. 36 
i 6.21 
6. 29 
i 6.27 
6. 27 
1 6.07 
6. 08 
