Four annual herbaceous species of Solanaceae were subjected to a comparative anatomical study on their stems at different growth successive stages. The main obtained results could be summarized as follows : 1- The extent of persistence of the epidermis during secondary growth of the stem differed according to the studied species. It may persist until the end of vegetative growth or may be substituted by a periderm initiated within timing of the periderm formation and extent of its development differed in the investigated species. 2- The clear manifestation dilatation growth in the extraxylary tissues of the stem differed according to species, depending probably on the rate of this process. 3- Pith diameter in the stem may remain unchanged after secondary growth, or it may largely decreased, according to species.