a black cloth "blanket" or wrapped in layers of aluminum foil. Dish 2 is exposed to lighl for 5 m 



then placed in darkness. 



3. Treatments: 



(a) Dish 1 remains in darkness throughout the demonstration and serves ae the dark control 



(b) Dish 2 is given its 5-minute irradiation immediately after distribution of the seeds, then placed in 

 darkness. 



(c) Dish 3 is irradiated for a period of 5 minutes with light from the fluorescent lamps after th< 

 have imbibed in darkness for a period of 1 hour; that is, the seeds are exposed to light 1 hour after 

 soaking. 



(d) Dishes 4, 5, 6, 7, and 8 are exposed to 5 minutes of light after 2, 4, 8, 16, and 24 hours, respectively, 

 of imbibition in darkness. 



4. After the 5-minute exposure to the fluorescent light the dishes are returned to the black cloth bags. 



5. Four days after the seeds were planted, the dishes can be removed from the dark and the number of 

 germinated seeds counted and recorded. 



OBSERVATIONS: 



Count the number of seeds germinated in each dish and record as percentage of germination. These data can 

 be presented in a line graph by plotting percentage of germination against the number of hours of imbibi- 

 tion. The results may show the sensitivity of the seeds to a given dose of light after certain periods of imbi- 

 bition without light. 



SUPPLEMENTARY READING: 

 See Demonstration A-l. 



DEMONSTRATION A-4: How a light requirement for germination can be 

 induced in seeds that normally do not require light for germination. 



MATERIALS: 



1. Seeds of various kinds of plants, including several varieties of lettuce and tomato. 



2. Four petri dishes or plastic sandwich boxes, with lids, for each kind of seed. 



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



4. At least one black sateen cloth bag, made of two layers of cloth, large enough to hold at leasl two 

 dishes (each containing a different kind of seed). 



5. Dark blue cellophane. 



6. Fluorescent lamp (a fluorescent desk lamp will do). 



PROCEDURE: 



1. Prepare the dishes as described under demonstration A-2. 



2. Four dishes should be used for each kind of seed tested. 



3. Treatments: 



(a) Dish 1 is placed in a black cloth bag (darkness). 



(b) Dish 2 is placed under the fluorescent lamp. 



(c) Dishes 3 and 4 are completely covered with two layers of a dark-blue cellophane filter and placed 

 under the fluorescent lamp. 



4. The fluorescent lamp is left on continuously. 



5. After germination is apparent in dish 2, count and record the number of germinated seeds in all dishes. 



6. Re-cover dish 3 with the blue cellophane and replace dish i> and dish 1 (without cellophane 1 under the 

 fluorescent lamp. 



7. When germination is completed in dish 1, count and record tin- germinated seeds in both dishes 3 and t. 



OBSERVATIONS: 



The seeds in the dishes under the dark blue cellophane may not germinate, whereas those receiving either 

 light or darkness may germinate nearly HK> percent. After a dish has remained under blue cellophane in light 

 for 3 or 1 days it can then be covered with black cloth and the seeds may remain dormant in the dark. When 

 subsequently given unfiltered light, they promptly germinate 



9 



