When we peel an orange, or walk in a rose garden, or rub a lavender sprig between our fingers, we distinguish with our olfactory ability, a special sensation of these plants. But what exactly is it that we can smell? More generally, it is essential oils that give spices and herbs their own feel and taste, or flowers and fruits, that give their own aroma. The essential oil of an orange peel is not difficult to identify. It exists in such abundance, that when we peel an orange, the essential oil "shoots" from the pores of the skin. However, the amount is so small that it evaporates immediately, leaving its characteristic aroma to linger. However, not all plants have essential oils in such abundance. The aromatic content of a rose is so little that it takes a ton of petals to produce 300g of oil. The reason why some plants contain essential oils while others do not is not yet fully understood. It is clear that the aromatic quality of oils plays a role in attracting or repelling certain insects or animals. One conclusion is that they play the role of actualizing life, which evolves through the plant itself, and the role of protection against disease. Essential oils have been described as the "hormones" or "souls" of plants because of their concentrated ethereal nature. Aromatic oils can be found in various parts of a plant, such as seeds, bark, root, leaves, flowers, wood, balsam and resins. For example, from an orange tree, the oil is produced from the peel of the fruit, petitgrain oil from the leaves and twigs, and neroli oil from the neroli flowers. Clove produces different types of essential oils from the buds, stem and leaves, while Scots pine produces it from the needles, wood and resin. The wide range of aromatic materials is sourced from natural sources and the art of extracting and using it has evolved slowly over time, but the origins reach far back into the heart of the most ancient civilizations.