The two diterpene (Z)-abienol and alpha and beta cembratriene-diols, the main diterpene constituents of the leaf exudate of tobacco, are widely distributed in varieties of Nicotiana tabacum. Although not in themselves aromatic, their degradation products impart an aromatic quality to smoke. Their production is affected by a certain number of agro-ecological factors, and by hereditary factors. The production of (Z)-abienol is under the control of a single dominant gene. By contrast, the synthesis of the alpha and beta-cembratriene-diols depends upon two genes of equal dominance. Knowing the mode of heredity of these two diterpenes allows an easier breeding of new varieties.