rocket (Barbarea vulgaris), tumble-mustard (Sisymbrium altissimum), 
chickweed (Stellaria sp. and Cerastium sp.), sheep sorrel (Rumex 
acetosella), the small-seeded cacti, and many others. 
2. Four dishes should be used for each kind of seeds tested. 
3. Cut the blotters to fit the dishes and presoak overnight (about 16 hours) 
by putting enough tapwater into the dishes to flood the blotters. 
4, After the blotters are thoroughly soaked, pour off the excess water and 
evenly distribute 100 seeds over the surface of the blotters in each dish, 
5. Immediately after the seeds are distributed, cover the dishes with their 
lids and place them in the black cloth bags. 
6. Allow the seeds to imbibe water in the dark for a period of 16 to 24 
hours, then begin treatments. 
7. Treatments: 
(a) Dishes 1 and 2 should be kept at about 709 F, during the entire period 
of the demonstration. Dishes 3 and 4 should be held at about 60° 
during the 16- to 24-hour imbibition period, then transferred to a 
temperature of 77°for the remainder of the demonstration. 
Dishes 1 and 3 are placed in the black cloth bags at the time of 
planting and left there throughout the demonstration. These will 
serve as ''dark controls,"! 
Dishes 2 and 4 should be placed in the light for 1 hour each day. 
The temperature during the period of irradiation can be between 70° 
and 80°. Light from two 40-watt standard cool-white fluorescent 
lamps should be adequate. 
(d) When the seeds in dishes 2 and 4 have germinated, the other dishes 
are removed from the black cloth bags andthe number of germinated 
seeds counted and recorded for each treatment. 
(b 
— 
— 
(c 
Observations: 
Record the number of days required for germination, the temperature, light 
conditions, and so forth. Count the number of seeds that germinate under 
each treatment and record as percentage of germination. When a light- 
senstitive seed is found, demonstrations can be designed to determine how 
much light the seeds require, how many times they must be exposed to 
light, and other data. These seeds can also be used in demonstrations 3, 4, 
and 5, 
Supplementary Reading: 
See Demonstration A-1. 
DEMONSTRATION A-3: Effect of duration of imbibition period (soaking) on 
effectiveness of a given light exposure in promoting 
germination of light-sensitive seeds. 
Materials: 
1. Eight petri dishes or plastic sandwich boxes with lids. 
2. Two to four thicknesses of blotters, filter paper, or paper towel cut to 
fit the dishes. 
Vy 
