The natural fragrance of flowers counts among the simpler pleasures in life. The delicate aroma of a rose in bloom is something that does not require explanation; we enjoy it simply and intuitively. In fact, to explain in scientific terms just what accounts for a flower's fragrant smell might sort of ruin the experience. But we're gonna do it anyway.
A flower's unique smell results from a combination of chemicals, including a large family of molecules called terpenes. Many terpene molecules produced by plants are volatile, which means that we can smell them. For example, volatile terpenes contribute to the aroma of lemons, mint, and turpentine. Many flowers produce specific mixtures of volatile terpenes to produce their specific odors.
Although these odiferous chemicals were originally only by-products of photosynthesis, through mutation and evolution they came to play an important role in pollination. A mutated gene causing a particular flower to produce a scent might give that flower a reproductive advantage by attracting insects necessary for pollination. Over time certain species of flowers developed unique smells to attract particular insects. For example, sweet-smelling flowers such as roses are engineered to attract butterflies. Some flowers even smell like rotting flesh in order to attract flies--not exactly the best choice for a corsage.
Maybe knowing something about the science behind flower fragrance will make the experience even more pleasurable. If not, clear your mind, inhale, and simply enjoy.