xi, c , 5 Copeland: Growth Phenomena of Dioscorea 233 
shoot and so tests the possibility of growing into thoroughly 
favorable conditions, following a different line. If this be the 
explanation, the dying of the tips in darkness may be a more 
pronounced expression of the same power of the plant to test 
out a succession of possible lines of growth, instead of consuming 
its whole food store in an attempt to reach the light with a single 
attempt. I have observed that branches of Dioscorea luzonica, 
growing beside my house, reach a limited length and stop rather 
abruptly under the eaves, but continue to grow much longer and 
develop as vegetative shoots, if they happen to grow outside the 
eaves. 
Direct, but not very careful, observation seemed to show that 
the plants in the laboratory grew as fast during the day as 
during the night or somewhat faster during the day. Doctor 
McLean kindly checked this observation by the use of the auxa- 
nometer with one of the healthy plants of Dioscorea hirsuta, No. 
331. The results of this test, from 9 o’clock in the morning, 
May 30, to 9 o’clock in the morning, May 31, with the thermo- 
graph reading at the same hours, are shown in Table V. 
Table V . — Hourly growth of a healthy plant of Dioscorea hirsuta, No. 331, 
during twenty-four hours. 
Time. 
Growth. 
Tempe- 
rature. 
Time. 
Growth. 
Tempe- 
rature. 
a. m. 
mm. 
°c. 
p. m. 
mm. 
•c. 
9 
27 
9___ 
6.8 
27.8 
10 
6.8 
27.6 
10 
8.7 
27.0 
11 
8.8 
28.5 
11 
7.8 
26.3 
m. 
12. 
7.5 
25.8 
12 
8.9 
29.5 
a. m. 
p. m. 
i 
6.5 
25.5 
l... 
9.1 
30.1 
2 
7.3 
25.2 
2 
8.4 
30.8 
3 
7.0 
25.0 
3 
10.1 
31.0 
4 
6.0 
24.9 
4 
11.3 
31.1 
5 
cn 
CO 
24.7 
5 
11.6 
31.1 
6 
6.6 
24.7 
6 
11.6 
30.6 
7 
6.3 
25.9 
7 
9.5 
29.8 
8 
5.9 
26.7 
8 
9.2 
28.6 
9 
6.4 
26.9 
' The growth of this plant during the daylight hours was conspic- 
uously more rapid than during the night, but the distribution of 
growth is very evidently much more closely correlated with the 
temperature than with the illumination, which was stronger 
during the forenoon than in the afternoon. The slowest growth 
recorded for any hour was from 7 to 8 in the morning, while the 
