The wavelength of light absorbed by the $P_r$ form of phytochrome is (in $nm$)

Photoperiodic stimulus is received by

The phenomenon where flowering is dependent on exposure to low temperatures is known as:

Winter varieties of wheat and barley are planted in

Nicotiana tabacum,a short-day plant,when exposed to more than the critical period of light,fails to flower. Explain.

$A$ group of plants flowered when exposed to a $12$ hour day and $12$ hour night cycle. Another group of the same plants did not flower when exposed to the same day-night cycle but with a brief light interruption during the night. What type of plants are these?