CBSE Class 10 Answered

The plants in order to flower require a certain day length i.e., the relative length of day and night which is called as photoperiod. The response of plants to the photoperiod expressed in the form of flowering is called as photoperiodism.

Florigen is a hypothetical flowering hormone. There are live plant growth hormones: gibberellins, cytokinins, abscisic acid and ethylene. Some plant physiologist suggested that some of these hormones might be acting as florigen.  

Role of hormones:

• Application of auxin causes flowering only in one of the short day plants pineapple.
• Gibberellin causes ffowering only in rosette long day plant. GA causes flowering in only one short day plant.
• Abscisic acid and ethylene also cause flowering in few species.