894 
Journal of Agricultural Research voi. xxm, No.» 
tubers. The details of the experiments are summarized in part in Table 
VI. All plantings were harvested September 26. Cinnamon vine, like 
Peking soybeans, responds very promptly to the decrease in length of 
day beginning with the summer solstice, only that the response takes 
the form of tuberization of aerial axillary buds instead of flowering. 
Under the natural length of day the aerial tubers appear one month after 
the summer solstice, and this holds true for the progenies of both the 
aerial and the larger subterranean tubers. By exposure to an artificially 
shortened day length of 13 hours or less, beginning at the summer solstice, 
the appearance of aerial tubers was hastened by about two weeks. As is 
to be expected from the quick response to the first shortening of the day 
length following the summer solstice, the maximum effect in hastening 
the aerial tuberization is produced by a 13-hour day, further reduction 
in day length to 12, 11, or 10 hours being without effect. By exposing 
the plants to the reduced daily illumination period earlier in the season 
the date of appearance of aerial tubers is advanced accordingly. When 
the treatment is applied in the earlier stages of development, however, 
a longer period of time is required for the tubers to come into evidence 
than when considerable advance growth has been made. In all cases 
growth of the vine is quickly checked by exposure to the reduced day 
length. The effect is so pronounced that exposure to a length of day of 11 
hours or less causes dying back of the young tips of the vines. This dying 
back practically ceases with a day length of 12 hours. It was not practical 
to obtain actual weights of aerial tubers produced under the different 
conditions of illumination, but it was observed that these tubers were 
formed in greatest number and of largest size under the io-hour and 
11-hour daily light exposure. Under a light period of 12 hours or more 
there was increasing tendency toward continued vegetative growth, and 
reduced production of aerial tubers. There seem to be no marked, 
consistent differences in ratio between the weights of underground tubers 
and vines under the various light exposures. The underground tubers 
produced larger vines than the aerial tubers under the shorter light 
periods. 
Table VI .—Effect of differences in length of day on tuberization in cinnamon vine 
Kind of tubers 
planted. 
Num¬ 
ber of 
plants 
grown. 
Date of 
germina¬ 
tion. 
Date of 
beginning 
light 
treat¬ 
ment. 
so. 
Length of 
day to 
which 
exposed. 
Date of 
first ap¬ 
pearance 
of aerial 
tubers. 
Aver¬ 
age 
weight 
of 
tubers 
and 
vines. 
Aver¬ 
age 
weight 
of green 
vines. 
Aver¬ 
age 
weight 
of 
tubers. 
Ratio of 
tubers 
to 
vines. 
Ounces. 
Ounces. 
Ounces. 
Aerial.. 
X 
Mar. 22 
May 2 
8 hours_ 
June 20 
4 
iK 
zH 
7:1 
Do.... 
3 
.. .do..... 
...do..... 
10 hours... 
.. .do. 
10 
1 
9 
9 » 
Do..... 
x 
.. .do..... 
June 21 
.. .do. 
July 4 
6 
a 
4 
2 :i 
Do. 
a 
.. .do. 
July 23 
n hours... 
July 3 
iij£ 
SJ 4 
2.8:x 
Do.... 
1 
...do..... 
June ax 
...do.. 
July 2 
s 
3-3:1 
Do.. 
X 
...do..... 
.. .do. 
12 hours... 
July 7 
zH 
1 
2% 
2.5:1 
Do. 
I 
...do..... 
13 hours.. 
July 2 
4 % 
1 
3 /^ 
3.5:1 
Do... 
5 
.. .do. 
Controls. 
Full day 
July 21 
16 
4 
12 
3:1 
length. 
1-year-old under¬ 
X 
Apr. 27 
Mar. 22 
8 hours.... 
June 15 
sH 
iK 
4 
2. 7:1 
ground. 
Do. ... 
X 
Apr. 26 
July 23 
.. .do. 
July 23 
19 
9 
10 
1.1:1 
Do. 
I 
Apr. 27 
Mar. 22 
10 hours... 
June 23 
8 
2 
6 
3:1 
Do. 
I 
Apr. 21 
June 21 
.. .do. 
July 2 
2lJ^ 
13 
1.5:1 
Do. 
X 
Apr. 26 
...do. 
11 hours... 
July 8 
17 
7 
10 
1.4:* 
Do. 
I 
May 4 
.. .do. 
12 hours... 
...do. 
19JH1 
3K 
16 
4.6:1 
Do........ 
X 
Apr. 25 
.. .do. 
X3 hours... 
June 30 
18K 
4 y 
x 4 , 
3- x:x 
Do. 
3 
Apr.a6to 
Controls. 
Full day 
July 21 
18K 
7 
11% 
1. 7:1 
May 29. 
length. 
to 23. 
