In some plants,the cold treatment may be replaced by the application of

Give scientific reasons:
$(1)$ Photoperiodism is essential for flowering in plants.
$(2)$ Abscission (leaf fall,flower fall,fruit fall) increases the vitality of plants.

In short-day plants,flowering is induced by:

Which of the following pigments absorbs red and far-red light?

The stimulus for flowering is perceived by which part of the plant?

$A$ change from vegetative to reproductive phase in plants occurs in response to