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. Keep the temperature about 75° F. Allow 3 to 4 days for the apples to turn red, then remove the foil 

 and tape. 



OBSERVATIONS: 



The apple that has been completely wrapped in foil will still be green. The one covered except for holes in 

 the foil will also be green except where light has entered through the cut-out portions; here, the apple will 

 be red and may have a polka-dot appearance of red en 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 will show 

 green initials on a red apple. 



SUPPLEMENTARY READING: 



Downs, R. J. Photocontrol of anthocyanin synthesis. Wash. Acad. Sci. Jour. 54: 112-120. 1964. 

 Siegelman, H. W., and Hendricks, S. B. Photocontrol of anthocyanin synthesis in apple skin. Plant 



Physiol. 33 : 185-190. 1958. 

 U.S. Agricultural Research Service. How light controls plant development. U.S. Dept. Agr., Agr. Res. 

 8: 3-5. 1959. 



D. Duration of Light 

 DEMONSTRATION D-l: Photoperiodic control of flowering of short-day plants. 



MATERIALS: 



1. Plants of cocklebur, lambsquarters, scarlet sage variety America, or morning-glory variety Scarlett 

 O'Hara should be grown from seed 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 lambsquarters 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. 



2. Sterilized soil. 



3. A light-equipped chamber. Illuminate the chamber with at least two 40-watt fluorescent lamps. 



4. A dark chamber. 

 PROCEDURE: 



1. When the plants are large enough to use, divide them into lots A and B. 



2. Both lots should receive 8 to 10 hours of light daily in the light chamber. 



3. Place lot A in darkness at the close of each 8- to 10-hour light period. Place lot B (inside the light 

 chamber) 3 to 4 feet from a lighted 40-watt incandescent-filament lamp. 



4. If an electric time switch" is available, give lot B a total daily light period of 18 to 20 hours (8 to 10 

 hours of fluorescent light plus 8 to 10 more hours of incandescent light). 



5. If an electric time switch is not available, leave the incandescent-filament lamp on throughout the 

 night. 



6. Each morning resume the fluorescent light treatments for both lots A and B. 



7. Continue these daily treatments until flowerbuds are obvious. 

 OBSERVATIONS: 



Record date of planting, date treatments began, and length of the light and dark periods; also record how 

 many short days were required to induce flowerbud formation. 

 SUPPLEMENTARY READING: 



Doorenbos, J., and Wellensiek, S. J. Photoperiodic control of floral induction. Ann. Rev. Plant Physiol. 



10: 147-184. 1959. 

 Lang, A. Physiology of flowering. Ann. Rev. Plant Physiol. 3: 265-306. 1952. 

 Liverman, J. L. The physiology of flowering. Ann. Rev. Plant Physiol. 6: 177-210. 1955. 

 Naylor, A. W. The control of flowering. Sci. Amer. 186: 49-56. 1952. 



Parker, M. W., and Borthwick, H. A. Influence of light on plant growth. Ann. Rev. Plant Physiol. 

 1: 43-58. 1950. 



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