i 
Procedure: 
Ib Deane in pots of sterilized soil, water, and place at a temperature 
of 80° F. 
2. After 3 to 4 days the plants will begin to emerge from the soil. At this 
time all pots should be placed in the light chamber, where they should 
receive light from the fluorescent lamps for 8 or 10 hours each day. 
The temperature during this growing period should be 70° to 75°F, 
3. The first pair of leaves should be about half expanded 10 to 12 days 
after planting. At this stage of development the plants are ready to 
start on treatments. 
4, Divide the plants into three equal lots; A, B, and C, 
5. Place plants of lot A inthe dark at the close of the 8- to 10-hour light 
period. Place lots B and C under the red and blue cellophane (the far- 
red), Turn off the fluorescent lamps. 
6. Place a 100-watt incandescent-filament lamp 3 feet from the red- and 
blue-cellophane filter and turn it on for 15 minutes. 
7. Plants of lot B are moved in darkness to the dark chamber immediately 
after the 15-minute exposure to far-red. Plants of lot C are moved in 
darkness and placed under the box with the red-cellophane filter, which 
should be placed under the fluorescent lamps. 
8. Turn on the fluorescent lamps for 10 minutes, then move plants of lot C 
in darkness to the dark chamber. (Great care should be taken to assure 
that the plants receive no light of any kind after they are exposed to red 
and to far-red.) 
9. Return all plants to the fluorescent-light chamber the next morning. 
10. The treatments should be given daily until a response is obvious, re- 
quiring at least 5 days of treatment. 
Observations: 
Record date of planting, date treatments were begun, number of days treat- 
ments were given, and the durations of the light period, red exposure, and 
far-red exposure. Measure and record daily the length of the second 
internode, Data can be plotted as line graphs (length plotted against time). 
Three plots should be made: The control (lot A), the far-red treatment 
(lot B), and the far-red followed by red (lot C). 
Supplementary Reading: 
Downs, R. J., Hendricks, S. B., and Borthwick, H. A, Photoreversible 
control of elongation. of Pinto beans and other plants under normal 
conditions of growth. Bot. Gaz. 118: 99-208. 1957. 
Wassink, E. C., and Stolwijk, J. A.J. Effects of light quality on growth. 
Ann, Rev. Plant Physiol. 7: 373-400. 1956. 
C. Light and Plant Pigments 
DEMONSTRATION C-1: Effect of light on formation of anthocyanin in seed- 
lings. 
Materials: 
1. Seeds of Wheatland milo, dwarf milo, or Sumac sorgo. 
2. Five petri dishes or plastic sandwich boxes with lids. 
18 
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