Why do flowers have a scent?
Gerald Klingaman, professor and extension specialist in the department of horticulture, replies:
Plants persist because they have developed an array of strategies to produce seeds. Attracting pollinators is an important part of the flower’s job, and it may achieve this attraction by the shape of the flower, its color or by its smell. Some species use only one of these methods; others use all three. For example, some orchids use fragrance to signal pollinating insects that a receptive flower is in the vicinity. Then, as the insect gets close, the color of the flower will attract it still closer. In some species, the orchid flower may have a peculiar shape that is marked just like a female of the species.
The compounds causing scent are specific blends of highly volatile chemicals such as terpenes, esters and oxygenated carotenoids that are released from specialized cells called osmophores. These special cells may be scattered evenly across the surface of a flower petal or concentrated in one area. Depending on the mixture of chemicals produced, the fragrance may be very pleasant and agreeable or very disagreeable. The carrion cactus of South Africa and the voodoo lily of Indonesia are pollinated by blow flies and smell like decaying flesh.
Many flowers that are pollinated by bees have a fragrance only during the early morning hours when bees are active, while flowers pollinated by moths often have fragrance only in the evening.