May 3,1924 
Photoperiodism of TepJirosia Candida 
453 
shown by plants in cans No. 8, which were planted March 29 and measured 
September 13, the B series measuring 823^, 89, and 93 inches in height, and the 
A series, 493^, 533^, and 54 inches. (PI. 4, B.) These measurements showed 
individually and collectively that a reduction of day length to 10 hours had 
greatly retarded apogeotropic growth. 
The opposite effect, 
achieved by lengthening 
the days, was shown by 
the plantings of August 
16 in cans No. 18. Those 
of the A series were sub¬ 
jected to a 10-hour daily 
exposure for a little over 
12 weeks after planting, 
that is until November 
10. At this time they 
averaged 12.7 inches in 
height, while the control, 
with exposure to normal 
daily length, averaged 
15.1 inches in height. 
The plants in the A ser¬ 
ies were subjected to a 
daily exposure of 13 i 
hours during 10 weeks, 
from November 10 to 
January 19, at the end 
of which time they aver¬ 
aged 52.6 inches in 
height, while the control, 
with exposure to normal 
day length, averaged 
only 35.9 inches. The 
growth of these plants 
up to a little more than 
24 weeks from planting 
is graphically shown in 
figure 5. 
EFFECT OF DAY 
LENGTH ON IN- 
TERNODAL 
LENGTH AND 
LEAF DIMEN¬ 
SIONS. 
In order to determine 
the effect of day length 
on internodal length and 
leaf dimensions, the 
plants in cans No. 1 to 
24, inclusive, were divided into four groups, cans No. 1 to ( 
18, and 19 to 24, respectively. Each group was measured 
Fig. 5.- 
Average increase in height made by 3 plants each in cans No. 
18, A and B series, under different light exposures. 
, 7 to 12, 13 to 
on the date on 
which its plants ranged from 12 to 22 weeks from planting. Prior to the taking 
of these measurements, the plants in the A series had uniformly received a 10- 
hour day length, and those in the B series, the normal day length. The tallest 
plant in each can was selected for measurement. Its height to the uppermost 
expanded leaf, number of nodes, and internodal length, are given in Table III. 
