DEMONSTRATION B-3: Why plants bend toward light (phototropism). 
Materials: 
1a 
A chamber or box that can be made completely dark. (See Demonstra- 
tion B-2, steps 1 through 4 of Materials, for details.) 
Procedure: 
Le 
Z. 
Plant the bean seeds; then water. No nutrient solution is required even 
when the seeds are planted in sand, Vermiculite, or Perlite. 
The best temperature is 80° to 85° F. Lower temperatures will suffice, 
but the rate of germination and growth will be slower. 
After the beans are planted, place one box in the dark chamber and one 
in the light, where the plants should receive 8 hours of light per day. 
When the dark-grown beans are about 6 days old, open the door of the 
dark chamber so that the plants receive some light. Better results are 
obtained by placing a desk lamp 3 or 4 feet from the open door of the 
chamber, 
When the plants in the light have expanded their first pair of leaves, 
place them in the dark chamber. Again, openthe door of the dark cham- 
ber and place a desk lamp 3 to 4 feet from the door. 
Observations: 
After a few hours the leaf blades will have twisted around until they are 
perpendicular to the light. 
Supplementary Reading: 
Textbooks of Plant Physiology. 
DEMONSTRATION B-4: Effect of red and far-red light onelongation of stems 
of light-grown plants. 
Materials: 
A light-equipped chamber (two 40-watt fluorescent lamps isa minimum), 
A red chamber (a cardboard box with seams sealed with paper tape). 
Cut out the top and most of the bottom of the box. Place two layers of 
red cellophane over the opening in the bottom of the box, using cello- 
phane tape to hold the cellophane in place. 
A far-red chamber (a cardboard box prepared in the same manner as 
for the red chamber except cover the cutout opening in the bottom with 
two layers of red and two layers of dark-blue cellophane). 
A dark chamber. 
Bean plants (preferably Pinto bean), 
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