2. Black cloth bags. 
3. Black plastic electrical tape. 
4, Aluminum foil. 
Procedure: 
1, Place one apple ina black cloth bag. 
2. Wrap one apple in aluminum foil, then cut holes in the foil and place 
the apple under the light of the growth chamber. 
3. Using the black plastic electrical tape, put an initial on each of several 
apples and place the apples under the light of the growth chamber. 
4. Allow 3 to 4 days for the apples to turn red, then remove the foil, tape, 
or black bag. Keep the temperature about 75° F, 
Observations: 
The apple that has been kept inthe dark will still be green. The one covered 
with aluminum foil will also be green except where light has entered through 
the cut-out holes; here, the apple will be red and may have a polka-dot 
appearance of red on green. The apple that was exposed to light except for 
areas under the black tape will be red, Under the black tape the apple will 
be green and thus show green initials on a red apple. 
Supplementary Reading: 
U.S. Agricultural Research Service. How light controls plant development. 
Us: Dept. Agr:, Agr. "Res..8: 35,00 959% 
Siegelman, H. W., and Hendricks, S. B. Photocontrol of anthocyanin 
synthesis in apple skin. Plant Physiol.“33: 185-190. 1958. 
D. Duration of Light 
DEMONSTRATION D-1: Photoperiodic control of flowering of short-day 
plants. 
Materials: 
1, A light-equipped chamber (two 40-watt fluorescent lamps isa minimum), 
2. A dark chamber. 
3. Plants of cocklebur, lambsquarter, scarlet sage variety America, or 
morning-glory variety Scarlett O'Hara should be grown on daylengths 
of 18 hours or more until large enough to use in the demonstration. Use 
morning-glory plants as soon as the cotyledons have expanded, Plants 
of cocklebur and lambsquarter are large enough when they have three 
leaves above the cotyledons. Photoperiodic treatments of scarlet sage 
can be begun as soon as the plants have 4 to 5 pairs of leaves. 
4, Sterilized soil. 
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