Flower initiation indicates a change over from the vegetative to reproductive phase of a plant. As already mentioned, a period of continuous vegetative growth is followed by a state called ripe to flower or a state of readiness for reproductive growth. Here, some stimuli are needed for the change over from vegetative to reproductive phase.

The stimuli change the gene programming of the vegetative shoot apex. Floral genes are activated and it is transformed into a reproductive shoot apex. Floral primordia are initiated. They differentiate into flowers.

The intervening period of vegetative growth necessary for transition from juvenility to ripeness to flower, varies in different species. To some extent, it is modified by the environment. But, the genetic makeup controls it completely. The duration may be one day, a few weeks, several months or even several years after germination.

The flowering behaviour of different plant species exhibit variation annual and biennial species die after flowering. Some perennial plants like Bambusa also flower once in its life time and then, die. Such plants are called monocarpic. .While other plants continue to flower periodically several times during their lifespan and are called polycarpic.

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Generally the schedule for flowering of a plant is definite and it can be predicted. The physiological mechanism responsible for flowering of plants are determined by (i) duration of its exposure to light in the day (ii) the environmental temperature and (iii) plant age.