DEMONSTRATIONS 
A. Light and Seed Germination 
DEMONSTRATION A-1: Effect of light on germination of seeds planted in soil. 
Materials: 
1. Seeds of peppergrass (Lepidium virginicum or 16 densiflorum). 
2. Sterilized potting soil. 
3. Six clay pots, or other suitable containers, 3 to 4 inches in diameter, 
4, Small glass squares large enough to completely cover the tops of the 
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pots. 
Glass baking dish or enamel pan large enough to contain all the pots, 
Pot labels. 
Procedure: 
lp. 
Fill six pots or containers with moist (not wet) sterilized soil to within 
2 centimeters of the top of the pots. Smooth the soil surface and tamp 
the soil gently but firmly with the bottom of one of the pots. 
Prepare six lots of 100 seeds each and distribute each lot of seeds uni- 
formly over the surface ofthe soilineach pot. Treat the pots as follows: 
(a) Pot 1 - leave the seeds on the surface. Do not cover them with soil. 
(b) Pots 2 to 6 - cover the seeds with 1 centimeter of soil. Level the 
soil surface and tamp gently. 
Do not water the top surface of the soil. Place all the pots in the large 
glass dish or enameled pan and subirrigate the soil inthe pots by 
adding water to the dish. Maintain the pots in this dish, being careful to 
have them setting in about 1 centimeter of water at all times. 
Place all pots in the light. 
Keep each pot covered witha glass square, at least until the seedlings 
that will develop are well established. The soil will be kept moist by 
capillary action. The glass cover will admit light but will prevent 
excessive water loss from the soil and maintain a high humidity at 
the soil surface, This is important during the critical periods of 
germination and early seedling growth. 
Write the name of the plant material, the date of planting, the date of 
treatment on a label, and insert it into the soil at the edge of the pot. 
Treatments: 
(a) Pot 1 - see 2a, 
(b) Pot 2 - see 2b. 
(c) Pot 3 - Immediately after covering the seeds with soil make a 
narrow slit 3 to 4 centimeters deep in the soil across the diameter 
of the pot with a knife. 
(d) Pots 4, 5, and 6 - repeat the process described for pot 3, 1, 2, and 4 
weeks after planting, respectively. 
