SUPPLEMENTARY READING: 



See Demonstration A-l. 



DEMONSTRATION A-5 : Photoreversible control of seed germination by red and 



far-red light. 



MATERIALS: 



1. Light-sensitive seeds such as Grand Rapids lettuce or peppergrass (Lepidium virginicum) . 



2. Three petri dishes or plastic sandwich boxes, with lids. 



3. Two to four thicknesses of white or colorfast blotters, filter paper, or paper towels. 



4. Black sateen cloth bags, made of two layers of cloth, large enough to hold each dish. 



5. Red and dark-blue cellophane. 



PROCEDURE: 



1. Cut the blotters to fit each dish and presoak overnight (about 16 hours) by putting enough tapwater into 

 the dishes to flood the blotters. 



2. After the blotters are thoroughly soaked, pour off excess water and evenly distribute 100 seeds over the 

 top blotter in each dish. 



3. Immediately place the dishes, with lids on, in the black cloth bags. Hold temperature as close to 70° F. 

 as possible. 



4. Allow the seeds to imbibe water in the dark for a period of 16 to 24 hours, then begin treatments. 



5. Treatments: 



(a) In the dimmest light possible, preferably complete darkness, remove dishes 1 and 2 from their black 

 cloth bags and wrap each dish with two layers of red cellophane. 



(b) Place both the cellophane-wrapped dishes under fluorescent light for a period of 5 minutes. 



(c) Return dish 1 to its black cloth bag without further exposure to light. If no dark room is available 

 during this transfer, place the dish in the black cloth bag without removing it from the 

 red cellophane. 



(d) Dish 2 is wrapped in blue cellophane so that the seeds are now covered with two layers of red and 

 two layers of blue cellophane. 



(e) Dish 2 is now exposed to light from the incandescent lamps for a period of 15 minutes. 



(f) Place dish 2 in the black cloth, either in complete darkness or if necessary still enclosed in the red 

 and blue cellophane. 



6. The three dishes of seeds have now received their treatments. Dish 3 has remained in the black cloth bag 

 and serves as a dark control. Dish 1 has been exposed to red radiant energy for 5 minutes and dish 2 has 

 been exposed to red for 5 minutes and to far-red for 15 minutes. 



7. Allow 3 to 4 days to elapse, then remove the dishes from their black cloth bags and count and record 

 the number of germinated seeds. 



OBSERVATIONS: 



When counting the number of seeds germinated in each dish, record as percentage of germination. These 

 data can be presented in either tabular form or in a bar graph, using the bars for treatments and the height 

 of the bars as percentage of germination. Those seeds that remained in darkness will probably germinate 

 percent if peppergrass seeds were used, or 5 to 25 percent if seeds of Grand Rapids lettuce were used. Those 

 seeds receiving red light will probably germinate 90 to 100 percent for both species, whereas those receiving 

 red followed by far-red might germinate 5 to 10 percent for peppergrass, and 5 to 25 percent for lettuce. 

 Evidence has now been obtained to show that these seeds require light (red) for germination, and that the 

 potential germination induced by the exposure to red can be reversed by a subsequent exposure to far- red 

 radiant energy. 



SUPPLEMENTARY READING: 

 See Demonstration A-l. 



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