Mar. 17, 1923 
Further Studies in Photoperiodism 
875 
Tabi^B I.— Effect of length of day on growth of sorghums from tropical Africa and British 
India 
i 
Sli 
M 
(k 
tn 
Point of origin. 
Number 
of plants 
grown. 
Date of shedding first pollen. 
Average 
height 
August 17 
(inches). 
Stoolingor branching, 
August 17. 
io-hour day. 
£ 
tJ 
1 
Control. 
io-hour day. 
1 
1 
% 
Control. 
[ io-hour day. | 
13-hour day. | 
Control. j 
>> 
ce 
T 3 
3 
O 
X 
6 
| 13-hour day. 
*S 
S 
37x14 
Kano, North Nige¬ 
ria, lat. ia° N.... 
5 
3 
4 
Aug. a 
Nov. 39 
Dec. 14 
52 
30 
27 
Marked. 
Slight. 
None 
39449 
Calulo, Angola, lat. 
15® S. 
ia 
6 
e 
3 
14 
43 
33 
23 
None... 
None.. 
Do. 
3945 X 
Calulo, Angola. 
5 
5 
9 
5 
4 
Dec. X7 
17 
52 
33 
26 
...do.... 
. ..do... 
Do. 
43626 
Caunpore, India, 
lat. ao° N. 
< 
4 
, 
9 
Sept, as 
65 
66 
40 
... do.... 
.. .do... 
Do. 
30450 
Togo, German West 
9 
Africa, lat. N. 8 °.. 
5 
9 
7 
a 
Oct. 33 
Nov. is 
70 
4 * 
34 
Marked. 
.. .do... 
Do. 
39450 
Calulo, Angola. 
4 
5 
5 
3 
Dec. is 
Dec. 17 
54 
32 
«7 
None .. 
...do... 
Do. 
1 The varietal numbers are those of the Office of Foreign Seed and Plant Introduction, Bureau of Plant 
Industry. 
Roots of perennial wild sunflower (Helianthus giganteus L.) transferred 
to the greenhouse in October soon developed vigorous shoots. Under 
natural daylight conditions flower buds appeared early in April and open 
blossoms in May. With the natural daylight period lengthened by use 
of the electric light till May 26, flowering was inhibited and there were 
no indications of blossoming as late as July 1. 
Another wild sunflower, Helianthus angustifolius L., an eastern and 
southern species, was planted in the electrically lighted house January 27. 
Under the long daily light exposure the plants grew to a height of 6 to 7 
feet without flowering at any time during the year. Specimens trans¬ 
ferred to a daily light exposure of 10 hours, beginning September 2, 
began flowering October 4 (PI. 2, A). Another lot of the plants ex¬ 
posed to the natural day length, beginning September 2, also flowered 
as a result of decreasing day length but much later than those under the 
io-hour exposure. The plants remaining in the electrically illuminated 
house finally formed flower buds in November, but under the combined 
influence of the weak electric light at night and the natural light of the 
short winter days these buds were prevented from unfolding and remained 
in a practically dormant condition throughout the winter. 
Cosmos bipinnata Cav., planted November 1, was in flower December 
22 and attained a final height of 30 inches under the normal day length. 
Continuing the light period till midnight by means of the electric light 
until arrival of the long summer days inhibited flowering. Growth con¬ 
tinued until early October, and the plants had attained a height of 15 feet 
when forced into flowering by the decreasing day length. 
Klondike cosmos (Cosmos sulphurea L.) was planted April 22 and had 
germinated April 25. Under a io-hour day beginning July 6 flower buds 
were showing July 19, and the first blossoms were open August 1. The 
control plants exposed to the natural length of day first showed flower 
buds October 1, and the first open blossoms appeared October 14. 
Corms of blazing star (Liatris graminifolia Walt.) were transplanted to 
metal buckets March 27. Under a io-hour day the first blossoms opened 
