Germination studies are often made 
on blotters in petri dishes in order to 
facilitate handling, planting, and 
counting the seeds. If petri dishes 
are not available, plastic sandwich 
boxes with lids and filter paper or 
paper towels are good substitutes. 
Studies of the effect of light on 
germination of seeds imply that some 
of the seeds must be kept in the dark 
tommactimas sa, check ox ‘control, The 
term ''dark'' means ''total darkness,'' 
a complete absence of light. Bags of 
at least two layers of black sateen 
cloth provide the darkness required 
for the dark controls. These bags must 
be large enough to contain the dishes, 
with enough slack at the opening sothat 
a flap may be folded back to prevent 
entrance of light. Analternate method 
would be to cover the dishes with two 
or more layers of aluminum foil. 
Studies on the effect of light on 
various plant responses can be made 
in greater detail, using red and far- 
red! radiant energy. These wave- 
lengths are the most effective ones 
for regulating many plant responses 
to light and they can be obtained by 
using colored filters in conjunction 
with the proper light source. The 
fluorescent lamp emits considerable 
red but almost no far-red and is, 
therefore, used as a source of red 
light. A filter of two layers of red 
cellophane removes all visible light 
except red and since very little far- 
red is emitted by the lamp, the net 
result is reasonably pure red light. 
Incandescent-filament lamps emit 
considerable amounts of far-red and 
are thus good sources of far-red. The 
visible light is removed by appro- 
priate filters such as a combination 
of red and blue cellophane, The red 
cellophane absorbs all the visible light 
except red and the dark-blue cello- 
Phane absorbs red, However, neither 
1In Europe this would be referred to as near infra- 
red, 
color of cellophane absorbs far-red, 
so the radiation passing through the 
filter is, therefore, far-red. 
Seeds of trees, shrubs, orna- 
mentals, vegetables, grains, and 
grasses can be obtained from com- 
mercial seed sources that range from 
special seed supply houses tothe local 
hardware store. Many weed seeds are 
light-sensitive, and these can be 
gathered by the investigator. After 
the seeds are gathered they shouldbe 
stored dry ina refrigerator (about 
40°F.) until an appropriate time to 
begin the experiments because at 
higher temperatures they often under - 
go change in their light requirements. 
A good supply of seeds should be 
gathered to assure an adequate amount 
for possible additional experiments. 
Any difficulty in identifying the plants 
can be resolved with the aid of high 
school biology teachers, the botanists 
or horticulturists at State university, 
State agricultural experiment sta- 
tions, or agriculture extension 
specialists. 
Demonstrations A-1l through A-5 
tell us the following facts: 
@®Certain kinds of seeds require 
light in order to germinate, 
@The light requirement is not 
something that occurs only under 
a special set of experimental 
conditions, but occurs when seeds 
are planted in an ordinary way in 
pots of soil. 
@A light requirement can be in- 
duced in seeds that normally do 
not require light for germination. 
@The photoreaction that allows 
germination to proceed is re- 
versible; red radiant energy 
drives the reaction in one direc- 
tion and far-red drives it in the 
reverse direction. 
