Sept. 15, 1925 
Response of Plants to Length of Bay and Night 
559 
primary stem, which remained in the vegetative stage throughout 
the exposure to long days, necessarily passed through the lower por¬ 
tion oi the stem, which, nevertheless, continued in the flowering 
condition. Moreover, the same is true of the organic materials 
passing from the upper vegetative portion of the stem downward to 
the roots. 
The initial experiment having given such interesting results, it 
seemed desirable to study further the possibilities in localizing the 
reproductive and vegetative phases of development in different por¬ 
tions of the axis in the individual plant. For this purpose a series of 
tests was conducted during the summer, when the days are long. 
To control the light exposures of the different parts of the plants 
light-proof boxes of suitable size, with three sides removable, were 
set up. Ventilation was provided for by inserting into the top and 
bottom or the upper and lower parts of the back of each box or com¬ 
partment a 3-inch galvanized-iron elbow to which were attached two 
similar elbows in such way as to form a double bend. These doubly 
curved pipes, blackened inside and outside, proved to be very satis¬ 
factory for the purpose in view. The top or bottom of each box, as 
required, was provided with a slot leading to an opening in the 
center into which the primary stem of the test plant could be slipped 
and the slot then closed. A front view of the cases, showing the 
S lants in position, is seen in Plate 3. The series of compartments 
ere shown make possible the exposure of top and bottom of the 
plant axis to different day lengths, the exposure of the central portion 
of the axis to a day length differing from that received by the upper 
and lower portions, and, finally, exposure of the upper part of the 
axis to continuous darkness day and night while the lower portion 
is exposed to a regulated day length. 
Seedlings of Cosmos svlphureus were grown during the spring 
months in a greenhouse in which electric light was used from sunset 
till midnight. Early in June the plants were set in 10-quart metal 
buckets and placed outdoors in preparation for the tests. As a 
control plant, to show the normal response to a short day, an indi¬ 
vidual was placed under a 10-hour day, beginning June 13, and the 
first blossom opened July 10. The appearance of the plant on 
July 16 is seen in Plate 1, 6. None of the plants left in the open 
showed any indications of flowering till October. The upper por¬ 
tion of the test plant shown in Plate 2, A, may be taken as illustrating 
the typical behavior when exposed to a long day. 
Beginning June 13, the upper portion of one of the plants was 
exposed to a 10-hour day while the lower portion was exposed to the 
full period of daylight. For this experiment the light-proof box 
shown in Plate 3, e , was used. This treatment was continued till 
September 23 when the plant was transferred to the greenhouse. On 
the upper portion of the plant exposed to the short day, flower buds 
could be seen June 25 and the first blossom opened July 9. No 
flowers or flower buds appeared on the lower portion of the stem, 
exposed to long days, except at the node immediately below the 
bottom of the box. (PI. 1, A.) At this node, which was about 1 inch 
below the base of the dark box, a single blossom opened August 11. 
Flower buds finally appeared in the lower portion of the stem October 
19, after the plant had been transferred to the greenhouse. 
