xi, c, 5 Copeland: Growth Phenomena of Dioscorea 237 
marks, growth should cease each day at the back end of the 
growing region, in zones having a total length about equal to the 
day’s total growth. I noticed years ago, that published figures 
by as careful a worker as Sachs do not stand this test, but that, 
if one might judge from the figures, the total elongating region 
is much longer on the second day than it was on the first. Since 
noticing this, I have always made it my practice to check meas- 
urements occasionally by remeasurement after a second day. 
This kind of check is illustrated by the measurements on plant 
“Light Soil No. 1,” Dioscorea hirsuta No. 331, May 23-25, shown 
in Table VII. 
Table VII . — Growth of the same zones on successive days. 
[Dioscorea hirsuta , Light Soil No. 1, May 23-25.] 
Centimeter zone. 
Growth, 
first day. 
Growth, 
two days. 
Centimeter zone. 
Growth, 
first day. 
Growth, 
two days. 
mm. 
mm. 
mm. 
mm. 
I 
5 
14 
6 
6 
2 
8 
15 
5 
5 
3 
12 
16 
4 
4 
12 
17 _ 
3 
5 
14 
18. 
2.5 
13.5 
6 
15 
19 __ 
2 
2 
7 
19 
34 
20 
2 
8 
19 
26 
21 
1.5 
9 
15 
17 
22 
1 
10 
14 
15 
23 
0.5 
11 
12 
13 
24 
0.5 
12 
9 
9 
25 
0.5 
13... 
8 
8 
26 
i 
Analyzing these figures, it appears that the growing region the 
first day was 25 centimeters long. At the end of the second day, 
zone 11 extended 25.4 centimeters from the apex, and was the 
last zone that showed any increase in length. In other words, 
the figures checked in this case and the length of the growing 
region was unchanged. 
Many of the plants in darkness had a short apical portion 
rather sharply bent. This was usually not more than 1.5 centi- 
meters in length. Repeated observation showed that the move- 
ment of these apical segments was quite irregular, which agrees 
with Newcombe’s observations. The most remarkable behavior 
shown was that of occasional plants that kept the bent part at 
nearly the same angle and in the same direction, while the stem 
as a whole was growing. The movement of this apical part 
resulted sometimes in a twisting of the stem and at the other 
times did not do so. Dioscorea alata is a remarkably convenient 
subject for the observation of twisting. 
