Why do flowers have fragrance?

Flowers are the (sexual) reproductive organs of the plant, housing the male and female reproductive organs of the plant. Sometimes both male and female parts are house in the same flower, in other instances there are seperate male and female flowers on the same plant, and in other instances seprate male and female plants.

The purpose of the flower is to attract polinators (insects, bats, animals etc.) to effect pollination - that is the movement of male pollen grains to the female sigma. Here the pollen grains germinate and eventually fuse with a female ovule which then develops into an embryo. The embryo then develops into a seed (above process is simplified!).

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