@Dormancy of woody plants in the 
autumn is brought about by short 
days. 
@ Daylength controls tuber and bulb 
formation as well as flowering 
and dormancy. 
Additional experiments can be de- 
signed to answer and demonstrate 
many other aspects of the photo- 
periodic control of flowering, bulbing, 
and dormancy. For example, we might 
ask, what is the critical daylength for 
short-day plants? What is the longest 
day (shortest night) that will induce 
flowering in short-day plants? What 
is the shortest day (longest night) that 
will induce flowering of long-day 
plants? When a long dark period is 
interrupted by a brief interval of light, 
what is the minimum energy required 
to keep short-day plants vegetative or 
to induce flowering of long-day 
plants? When is the most efficient 
time to give the interruption during 
the dark period? Is the control of 
flowering operated through the same 
red, far-red reversible photoreac- 
tion that controls other plant re- 
sponses? 
GENERAL CULTURAL HINTS 
For all demonstrations in which 
seeds are germinated in soil or in 
which young seedlings are to be grown, 
the soil should be sterilized, Steriliz- 
ing the soil destroys harmfulinsects, 
disease-producing organisms, and 
weed seeds. Soil may be sterilized by 
different methods: (1) Place small 
lots of moist soil in a shallow panand 
bake for at least 1 hour atatempera- 
ture of 215°F,, then cool but do not 
use for at least 2 weeks; (2) place 
soil in an autoclave or pressure 
cooker and steam sterilize at 15 
pounds' pressure for at least 1/2 hour, 
then allow to stand for a minimum of 
2 weeks; (3) sprinkle 1 quart of 
formaldehyde solution (1 pint 37 per- 
cent commercial formaldehyde to 3- 
3/4 gallons water) on 1 square foot 
by 6 inches of soil placed in a box or 
bushel basket, then water liberally 
and completely cover with plastic or 
heavy cloth for 48 hours, stirring 
frequently to hasten escape of the 
formaldehyde gas, and allow 2 weeks 
before use of the soil. (CAUTION: 
Do not use for planting as long as 
fumes are present, because formalde- 
hyde gas is an irritating poison to 
humans and is toxic to plants.) 
Plants are usually grown in clay 
pots of 3-, 3-1/2, or 4-inch diameter 
filled with sterilized soil. Before the 
soil is put into the pot a piece of 
broken pot is placed in the bottom to 
cover the hole so that the soil willnot 
plug it and prevent good drainage. 
Clean pots should always be used. 
When pots are not available or are 
for some reason objectionable, plastic 
cups, polyethylene freezer food con- 
tainers, or even tin cans may be used. 
One or more holes should be punched 
in the bottom of these containers and 
the holes covered with fiberglass 
matting or plastic window screen be- 
fore filling with soil. Good drainage 
is imperative for good plant growth. 
Studies of the effect of light on plant 
growth and flowering require that the 
plants be placed in darkness at cer- 
tain times, As with seed germination, 
this means complete or total dark- 
ness. Because plants require more 
space than seeds, light-tight bags are 
usually not satisfactory. Instead, a 
dark chamber must be constructed in 
such a way that there is adequate air 
exchange between the inside and out- 
side of the chamber to prevent over- 
heating. A satisfactory and proven 
method is to construct a frame of 
wood and cover it with at least two 
layers of black sateen cloth. An 
entrance or door can be provided by 
making an overlapping flap. 
