Take a deep breath! Orange, peppermint and basil help relieve the mind of its burdens, while lavender, patchouli and chamomile cool off the emotions. Essential oils are the highly concentrated, volatile, aromatic essences of plants. Scientists agree that essential oils may perform more than one function in living plants. In some cases they seem to be a part of the plant's immune system. In other cases they may simply be end-products of metabolism. Essential oils contain hundreds of organic constituents, including hormones, vitamins and other natural elements that work on many levels. They are 75 to 100 times more concentrated than the oils in dried herbs.