488 BOTANICAL GAZETTE [DECEMBER 
weight and 8.24 per cent of the dry weight on the concave side of ~ 
seedlings stimulated 45 minutes. 
The dry weight of the curved portion of the shoot (fig. 5, B) 
was determined for various times of stimulation. The material 
was split into concave and convex halves, weighed, and dried to 
constant weight in an electric oven at a temperature of 104° C. 
The differences obtained, while slight, are significant in that they 
vary in the same direction. Table VI explains itself. 



















TABLE VI 
Time Fresh wt. | Fresh wt. Dry Dry wt. | Percentage | Percentage : 
stim. concave convex pa convex dry wt. dry wt. Diff. 
days grams grams concave nvex 
aaa 22.0139 | 26.6482 | 1.2480 | 1.4234 5.44 5.34 0.09 
ees eee 17.0296 | 20.8236 .9202 1.0746 5-43 5.16 0.17 
AO, 54.1735 | 62.2810 2.8621 3: 1524 e306 5.06 0.14 
Summary 
1. The acidity of the growing shoot is greatest at the tip and 
decreases downward. 
2. The relative acidity of the two flanks of the geotropically 
stimulated shoots changes during presentation and reaction time. 
First the concave side becomes relatively more acid, then decreases 
until the maximum acidity comes to lie on the convex s'de. The 
two flanks now gradually become equal in acidity, this period coin- 
ciding with the time of visible curvature. This equality in acidity 
is maintained until the tip of the shoot has passed the vertical 
plane, when the concave side again becomes more acid. As the 
shoot straightens, the difference in acidity decreases. 
3. The increase of acidity does not pees the relative rate of 
growth on the two flanks. 
4. Several plants examined develop in neutral solution a chro- 
mogen which acts as a delicate acid-alkali indicator. 
5. The percentage of dry weight is greatest on the concave side. 
The writer is indebted to Dr. F. C. Kocu for peeoeasse in the 
method of sugar analysis. 
UNIVERSITY OF CHICAGO 
