Prolongation of continuous darkness will initiate

Phytochrome is:

Which chemical is associated with flowering?

Photoperiodism is associated with the formation of

The phytochrome was discovered by

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?