B. Light and Plant Growth 
DEMONSTRATION B-1: Control by light of the growth of an internode, 
Materials: 
ve 
Corn seeds, 
2. Two 4- to 5-inch clay pots or other suitable containers, 
3. Sterilized soil. 
Procedure: 
19s 
2. 
Place a piece of broken pot, fiberglass mat, or plastic screen over the 
drainage hole in the bottom of the pot or container. 
Fill pot or container 1 with sterilized soil to within 3 centimeters of 
the top of the pot, tamp the soil gently, place 3 to 4 corn seeds on the 
surface of the soil, and cover them with 2 centimeters of soil. Tamp 
firmly. 
Fill pot 2 with 3 centimeters of sterilized soil, tamp gently, place 3 to 4 
corn seeds on the surface of the soil, and fill the pot with sufficient soil 
to reach the same level as in pot 1. Tamp firmly. 
Place both pots in a large glass dish or enameled pan and subirrigate 
by adding water to the dish or pan. 
Place both pots in the light at atemperature of about 70° to 80° F. 
The seedlings of pot 1 will emerge first, Let them grow until the 
seedlings of pot 2 emerge and produce a leaf, 
Knock the soil out of the pots into a bucket of water and remove the 
seedlings from the soil, holding the soil and seedling under the surface 
of the water until the roots are free of soil. 
Observations: 
Compare and measure the length of the first internode (the distance from 
the corn seed to the beginning of the first leaf), Note that the internodes 
in both pots 1 and 2 stopped growing when the plant emerged from the soil; 
that is, when the seedling received light. 
Supplementary Reading: 
U.S. Agricultural Research Service. New light on plants. U.S. Dept. Agr., 
Agr, Res: 3-5. 1953. 
DEMONSTRATION B-2: Control by light of growth and chlorophyll formation. 
Materials: 
Le 
A chamber or box that can be made completely dark. If entrance into 
the chamber cannot be made without exposing the contents to light, 
regardless of how weak the light is, then more than one chamber will 
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