Have you ever wondered why some flowers, such as old fashioned roses have a lovely fragrance and others, especially some of the newer hybrids, have no fragrance? Personally I think all roses should have that great fragrance. It took a little digging, but in reading a vintage flower-grower’s handbook, I found a simple explanation that sheds some light on just what makes the fragrance in flowers – it is a part of a flower referred to as nectaries.

Not all flower fragrances are pleasant. The corpse lily emits a fragrance likened to rotting flesh. Skunk cabbages emit a fragrance indicative of their name. But flowering plants do not release fragrances for the benefit of our human noses. Flowers use their scents to attract pollinators and communicate with other plants. Many flowers emit scents to aid reproduction. Flowers use their ability to create fragrance to lure pollinators and provide them with nectar as a food reward. Nectar-feeding creatures include many species such as bees, butterflies, moths, flies, and even mosquitoes, bats and hummingbirds. For carnivorous plants such as the Venus Fly trap and Pitcher plant, fragrance lures in insects to be captured and digested within the flower cavity for food.

Some flowering plants are non-discriminating using their fragrances to attract a host of insects and birds to fertilize their flowers. Others specialize in releasing scents that only appeal to a particular insect. An example is a specific yucca that relies on a single "yucca" moth for its pollination. In pollination, an insect comes into contact with pollen bearing flower parts and takes some pollen with it before it leaves. It then unknowingly deposits that pollen on another flower of the same species, pollinating the plant and satisfying its need for production of a future generation through seed.

Until the past few decades, the biochemical process of fragrance production remained unknown. In 1953, chemists identified some 20 chemicals in a rose’s fragrance. By 2006, that number was roughly 400. The nectaries that create these chemical fragrances usually are found at the base of the male stamen inside the flower. To date, scientists have catalogued 1,700 different fragrance compounds produced by flowers, with some single plants having a mix of more than 100 compounds.

Nectaries secrete sugars and amino acids to form both nectar and fragrance molecules that are complex mixtures of low molecular weight compounds. Each fragrance compound is an organic molecule known as a volatile that vaporizes into a gas when released by the plant. These molecules are so small that if the average person had the same body size as the moon, the largest fragrance molecule would have the size of a marshmallow. Although flowers may appear identical in color or shape, no similar flowers have fragrances that are exactly the same because of the large diversity of volatile compounds that make up fragrance.

Fragrance is a signal that directs pollinators to a particular flower whose nectar or pollen is the food reward. Species pollinated by bees and flies have sweet fragrances, while those pollinated by beetles, for example, have strong musty, spicy, or fruity aromas. Little is known about exactly how insects respond to these compounds within floral scents, but it is clear that they are capable of distinguishing among the complex fragrance mixtures. Since much of our food production relies on insect-based pollination, think honeybees, we as humans therefore rely on a flower’s ability to produce fragrance for our food. Think about it.

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