B. Light and Plant Growth 



DEMONSTRATION B-l: Control by light of the growth of an internede. 



MATERIALS: 



1 . Corn seeds. 



2. Sterilized soil. 



3. Two 4- to 5-inch clay pots or other suitable containers. 



4. Glass baking dish or enameled pan large enough to hold the pots. 



PROCEDURE: 



1. Place a piece of broken pot, fiberglass mat, or plastic screen over the drainage hole in the bottom of the 

 pot or container. 



2. Fill pot or container 1 with sterilized soil to within 3 centimeters of the top, tamp the soil gently, place 

 3 or 4 corn seeds on the surface of the soil, and cover them with 2 centimeters of soil. Tamp firmly. 



3. Fill pot 2 with 3 centimeters of sterilized soil, tamp gently, place 3 or 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. 



4. Place both pots in the large glass dish or enameled pan and subirrigate by adding water to the dish or 

 pan. 



5. Place both pots in unfiltered sunlight at a temperature of about 70° to 80° F. 



6. The seedlings of pot 1 will emerge first. Let them grow until the seedlings of pot 2 emerge ami produce a 

 leaf. 



7. 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. 1: 3 -•">. L953 



DEMONSTRATION B-2: Control by light of growth and chlorophyll formation. 



MATERIALS: 



1. Bean seeds (any kind). 



2. At least five flats, boxes, pots, or plastic freezer cups filled with sterilized soil or sand or with Vermiculite 

 or Perlite. 



3. 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 several ehamb. 



for each container of plants) will 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. 



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 oi germination and 

 growth will be slower. 



3. Place the five boxes in the dark chambers immediately after tbe» beans are planted. Beans, planted in 

 sand and kept at 80° to 85°, will germinate in :> to I days. 



4. On the tilth day, place box 1 in the light (preferably from fluorescent lamps for 5 minutes, then return 

 it to the dark chamber. 



5. Repeat step 1 on the sixth, seventh, and eighth days from planting. 



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