3. Turn off fluorescent lamps. Place lot A in darkness at the close of each 
8- to 10-hour light period. Place lot Bin light from a 40-watt incandes- 
cent-filament lamp. 
4. If an electric time switch is available, allow a total light period of 16 
to 18 hours for lot B (8 to 10 hours from the fluorescent lamps and 
another 8 hours from the incandescent lamp.) 
5. If an electric time switch is not available, leave the incandescent lamp 
on throughout the night. 
6. Return both lots to the fluorescent-lighted chamber each morning. 
7. These treatments should be given daily until flower buds are obvious. 
During this period of development all plants should be grown on short 
days of 8 to 10 hours' duration, If the treatments are stopped at this 
point, the flower buds will usually continue to develop. 
Observations: 
Record date of planting, date demonstration began, length of the light and 
dark periods, and also record how many long days were required to induce 
formation of flowers. If the tuberous-rooted begonia is used as the experi- 
mental plant, make observations on the extent of tuber formation as well 
as flowering. 
Supplementary Reading: 
U.S. Agricultural Research Service. Prescription for better plant form. 
U.S. Dept. Agr., Agr. Res. 8: 14. 1959. 
See Demonstration D-1. 
DEMONSTRATION D-3: Photoperiodic control of growth and dormancy of 
woody plants. 
Materials: 
1. A light-equipped chamber, 
2. A dark chamber, 
3. Seedlings or rooted cuttings of some woody plant material such as 
deciduous trees (catalpa and red maple), evergreen trees (spruce, 
loblolly pine, slash pine, or Virginia pine), and shrubs (hollies and 
Weigela). 
Procedure: 
1, Divide rooted cuttings or seedlings into lots A and B and place both lots 
in the light chamber for 8 to 10 hours daily. 
2. Place lot A in darkness at the close of each 8- to 10-hour light period. 
3. Turn off the fluorescent lamps and place lot B 3 to 4 feet from a 40-waitt 
incandescent-filament lamp, which is now turned on, 
4, If an electric time switch is available, the total daily light period for 
plants of lot B should be 16 to 18 hours (8 to 10 hours of fluorescent 
light plus 8 more hours of incandescent light.) 
5. If an electric time switch is not available, leave the incandescent light 
on throughout the night. 
6. Return both lots A and B to the light chamber each morning. 
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