be needed, These chambers can be made of Masonite or plywood with 
calked seams and a baffled door, or they can be made of several layers 
of black sateen cloth stretched over a wooden frame, 
2. Two 40-watt fluorescent lamps. 
3. At least five flats, boxes, pots, or plastic freezer cups filled with 
sterilized soil, sand, Vermiculite, or Perlite. 
4. Bean seeds (any kind). 
Procedure: 
1. Plant the bean seeds; then water. No nutrient solution is required even 
when the seeds are planted in sand, Vermiculite, or Perlite. 
2. The best temperature is 80° to 85° F, Lower temperatures will suffice, 
but the rate of germination and growth will be slower. 
3. Place the five boxes in the dark chambers immediately after the beans 
are planted. Beans, planted in sand and kept at 80° to 859, will ger- 
minate in 3 to 4 days. 
4, On the fifth day, place box 1 in the light (preferably from fluorescent 
lamps) for 5 minutes, then return it to the dark chamber. 
5. Repeat step 4 on the sixth, seventh, and eighth days from planting. 
6. Place box 2 in the light for 20 minutes on the fifth day only. 
7. Place box 3 under the light for 2 hours each day, and box 4 for a period 
of at least 8 hours per day. 
8. Remove all five boxes from the dark chambers on the ninth or tenth day 
from planting. Measure and record the length of each internode and the 
length of the leaves. 
9, Slice or mince the leaves and place in a known volume of ethyl alcohol. 
Use the same volume of alcohol for each treatment irrespective of the 
size of the leaves. A better method is to use 10 milliliters of alcohol 
for each gram of leaves. 
10. Calculate the average length of the internodes and the average length 
of the leaves for each treatment, 
11, The relative amounts of chlorophyll can be estimated by assigning a 
numerical value to each sample based on the visual greenness of the 
extract, or by measuring the optical density of each sample. 
Observations: 
The plants grown in complete darkness (box 5) should have long hypocotyls, 
short first internodes, small leaves, and no chlorophyll. Boxes 1, 2, 3, and 
4 should contain plants that have shorter hypocotyls, longer first internodes, 
and perhaps more internodes than the plants of box 5. They should also have 
much larger leaves. Plants of box 1 shouldcontain no chlorophyll, and those 
of box 2 none or very little. Plants in boxes 3 and 4, however, should con- 
tain a greater amount of chlorophyll, withthose plants of box 4 having more 
than those of box 3, 
Supplementary Reading: 
Downs, R. J. Photoreversibility of leaf and hypocotyl elongation of dark- 
grown red kidney bean seedlings. Plant Physiol. 30: 468-473. 1955. 
Textbooks of Plant Physiology. 
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