Photoperiodism was first characterised in

Some varieties of wheat are known as spring wheat while others are called winter wheat. The former variety is sown and planted in spring and is harvested by the end of the same season. However,winter varieties,if planted in spring,fail to flower or produce mature grains within a span of a flowering season. Explain,why?

Phytochrome is associated with which of the following processes?

What do you understand by photoperiodism and vernalisation? Describe their significance.

At which wavelength is light absorbed by the phytochrome in the $P_r$ form (in $, nm$)?

$Nicotiana$ $tabacum$,a short-day plant,fails to flower when exposed to a light duration longer than its critical period. Explain.