876 
Journal of Agricultural Research 
Vol. XXIII, No. II 
June 2i, the plants averaging 17 inches in height. Under a 13-hour day 
blossoming began July 22, and the average height was 24 inches. The 
controls began flowering August 26 and were slightly taller than the 
13-hour day plants. In the following season a second lot of conns were 
transplanted from the field May 19 and exposed to different day lengths. 
Under a io-hour day flower buds were showing June 6, and the first open 
blossoms appeared July 2. The average height of the plants was 12 
inches. Under a 12-hour day flower buds could be seen June 6, and the 
first blossoms unfolded June 30, when the plants had attained a height 
of 12 inches. The controls were showing flower buds July 22 and first 
open blossoms September 12. The average height was 35 inches. 
Tithonia rotundifolia (Mill) Blake, planted January 4, was in bloom 
March 14 under natural daylight, having attained a height of 48 inches. 
In the greenhouse electrically lighted at night the height on March 14 
was 27 inches and there were no indications of flowering. Blossoming 
was inhibited indefinitely under these conditions. Seed were again sown 
April 6. The plants exposed to a io-hour day beginning June 3 were 
showing flower buds July 27 and open blossoms on August 13. The 
control plants under the full day length showed no flower buds as late 
as September 22. 
Roots of sorrel (Rumex acetosella L.) were transferred to the green* 
house October 12. Under natural day length aerial development was 
limited to abundant leaf formation, while under the artificially lengthened 
illumination period flowering stems were formed and pollen was falling 
January 19. Thereafter these latter plants continued as typical ever- 
bloomers. The plants under the short-day exposure, on the other hand, 
were very active in the development of underground stems, the soil of 
the container becoming thickly studded with this type of growth. 
When grown in the open bed in the greenhouse under the short-day con¬ 
ditions the plants produced underground stems 2 feet or more in length. 
Plants of roselle (.Hibiscus sdbdariffa L.) were subjected to a io-hour 
day when about 10 inches high, beginning July 20. First blossoms 
appeared September 11, whereas the control plants did not flower till 
early November. 
Cuttings of smartweed (Polyganum sp.) were set in moist sand June 
30. Under a io-hour light exposure the plants were in blossom July 21, 
while the controls showed no indications of flowering on August 18. 
The respective heights of the plants July 28 were 14 and 9 inches. 
A late fall variety of chrysanthemum was exposed to a io-hour day, 
beginning May 12, and was in blossom July 28, while the control plants, 
of course, did not flower till late fall. Under a 13-hour exposure flower¬ 
ing was about 3 weeks later than under the io-hour exposure. The 
io-hour day plants flowered freely and the blossoms were normal. 
A very late variety of dahlia, known as John Ehlich, was placed under 
a io-hour day, beginning May 12, and the first blossom opened July 8. 
Under the natural day length the first blossom opened September 27. 
^Specimens of poinsettia (Euphorbia heterophylla L.), 8 to 10 inches 
nigh, exposed to 10 hours of light daily after July 9 soon flowered, and 
in 5 to 6 weeks the tops of the plants were gorgeously colored. (PI. 19, A.) 
Similar plants exposed to 12 hours of light daily blossomed September 3, 
but the upper leaves reddened very slowly. The controls did not flower 
till November. The 12-hour plants eventually produced numerous viable 
