Photoperiodism was first characterised in

The pigment involved in red-far red light interconversion is

Which of the following is a long day plant?

Which of the following factors influence the process of flowering?

On germination,a seed first produces shoots with leaves,and flowers appear later.
$(A)$ Why do you think this happens?
$(B)$ How is this advantageous to the plant?

Assertion $(A)$: Vernalization is the acceleration of subsequent flowering by low-temperature treatment.
Reason $(R)$: The site of vernalization is the apical meristem.