This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
A small order with most of the structural characters of the last, but usually of erect habit and often arborescent. It is distinguished by having simple or pinnate opposite exstipulate leaves and usually small hermaphrodite and unisexual flowers, rarely apetalous (Frdxinus). Calyx inferior, 4-partite. Corolla of 4 petals. Stamens 2. Fruit a drupe, berry or capsule, 2-celled or by abortion 1-celled and 1-seeded. About 25 genera and 140 species are referred here. The members of this order are most abundant in the temperate and warmer zones of the north, but isolated species are found in the tropics and southwards. The Olive, Olea Europaea, is one of the most useful members of this group. Chionanthus Virginica, the Fringe Tree of North America, is a very ornamental tree with large simple deciduous leaves and drooping clusters of pure white flowers having narrow fringe-like petals, and followed by purple drupes; but it is very rare in cultivation in this country.