3. Eight black sateen cloth bags made of two layers of cloth large enough 
to hold the dishes. As an alternate method dishes can be placed between 
the folds of a large, double layer of black cloth, or they can be wrapped 
with two layers of aluminum foil. 
4, Light-sensitive seeds such as Grand Rapids lettuce or peppergrass 
(Lepidium virginicum). 
Procedure: 
1, Prepare the dishes as outlined in the procedure in demonstration A-2. 
Use 0.2 percent KNO3 instead of tapwater for peppergrass. 
2. All dishes except dish 2areimmediately placedin darkness (inthe black jj 
cloth bags or between folds ofablackcloth ''blanket''). Dish 2 is exposed 
to light for a period of 5 minutes, then placed in darkness, Illumination 
provided by two 40-watt fluorescent lamp is adequate. 
3. Treatments: 
(a) Dish 1 remains in darkness throughout the demonstrationand serves 
as the dark control. J 
(b) Dish 2 is irradiated immediately after distributing the seeds, then 
placed in darkness. 
(c) Dish 3 is irradiated for a period of 5 minutes with light from the 
fluorescent lamps after the seeds 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 of imbibition in darkness, 
4. After the 5-minute exposure to the fluorescent light the dishes are 
returned to the black cloth bags, to the folded black cloth blanket, or to 
the aluminum foil. 
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 andrecordas percentage 
of germination. These data can be presentedina line graph by plotting per- 
centage of germination against the number of hours of imbibition. The 
results may show the sensitivity ofthe seeds to a given dose of light changes 
during the period of imbibition. 
Supplementary Reading: 
See Demonstration A-1. 
DEMONSTRATION A-4: How a light requirement for germination can be in- 
duced in seeds that normally do not require light for 
germination. 
Materials: 
1, Petri dishes or plastic sandwich boxes with lids. 
2. Blotters, filter paper, or paper towels cut to fit the dishes. 
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