May 3, 1924 
Photoperiodism of Tephrosia Candida 
447 
It was noted that less than 2 per cent of the plants bore flowers on September 
12, but that budding was very general. Approximately 5 per cent of the plants 
were in blossom by September 19, one-fourth of the total number were in blos¬ 
som by September 26, and about one-half by October 3. Three-fourths of the 
total number were in flower or bore buds, which were about ready to open, by 
October 10. An examination of a half section of the field comprising 27 rows, 
one of the two rows planted on each planting date, showed that only about 8 per 
cent of the plants had failed to bloom by this time. Blossoming in the field was 
practically over by the end of the first week in November. 
The blossoming record of the two seasons shows that, with a day length favor¬ 
able to blossoming, practically all plants, except, of course, those weakened by 
age or disease, as old as 6 months (rows No. 10, planted April 26, 1922, the 
plants of which blossomed the following autumn), and a number only 4\ months 
old (rows No. 13, planted June 7, 1922), may be expected to bloom. The record 
also shows that plants that are much younger than 4\ months at the blossoming 
season will not only pass the first season without flowering, but will also not 
develop flowers until the return of the favorable day length the following year. 
This was exemplified by plants (rows No. 14 and higher) which, although planted 
June 21, 1922, and later, did not blossom until the autumn of 1923, when some 
were 15 and 16 months old. The results clearly show that the blossoming 
season of plants having reached a sufficient maturity is very definitely determined 
by the day length instead of by age. 
The record further shows that (1) there is, in the course of a year, only one 
comparatively short and very definite season of heavy blossoming which reaches 
its height in midautumn; (2) this season is followed by a period covering several 
months during which a very few scattered flowers may open on plants that 
have already blossomed; (3) although there are indications of budding in the 
spring or early summer, such budding, except in some few instances, is not fol¬ 
lowed by flowers after a sufficient lapse of time; and (4) vegetative growth is 
resumed and in turn is followed by blossoming at the samfc season as in the pre¬ 
ceding year. 
EFFECT OF VARYING THE DAY LENGTH ON BLOSSOMING 
In order to determine the effect on the plants of artificially protracting or 
shortening the length of daily exposure to light, a series of plantings was made 
in oil cans having a capacity of 5 gallons. The cans were uniformly filled with 
river-bottom loam. Three plants were grown to a can, two cans being planted 
with Tephrosia Candida simultaneously with each field planting, and correspond¬ 
ingly numbered with the rows planted the same day. One of each pair of cans 
was lettered “A,” and the other, “B.” The plants in the A series were exposed 
to varying day lengths. Those in the B series were exposed to normal day length. 
Since for the artificially shortened day the light exposure began abruptly, and 
for the artificially lengthened day terminated abruptly with the turning off of 
the electric light, a day artificially shortened or lengthened to 12 hours with 
only a single twilight exposure was shorter than the corresponding natural day 
of 12 hours between sunrise and sunset with its double twilight. 
To give the plants additional light exposure, the cans were placed below a 
framework, 4 by 6 feet, carrying 6 tungsten filament incandescent lights, each 
rated at 25 candlepower, set 3 by 4 feet. An adjustable screen and black cur¬ 
tain, provided to furnish two distinct exposures, effectively protected half the 
space from the light used by the other half when two of the lights at one end 
were switched off. It being feared that the intensity of light was insufficient, 
the two middle lights were replaced by two of 60 candlepower at the end of the 
seventh week of lighting, and one at each end was replaced by one of 40 candle- 
power 9 days later. 
