The New International Encyclopædia/Arbor Vitæ

AR'BOR VI'TÆ (Lat., tree of life), Thuja. A genus of plants of the order Coniferæ, allied to the cypress, and consisting of evergreen trees and shrubs with compressed or flattened branchlets—small, scale-like, imbricated leaves. Species of arbor vitæ are found in the north temperate zones of both hemispheres. The common arbor vitæ (Thuja occidentalis) is a native of North America, especially between latitude 45° and latitude 49°, but has long been well known in Europe. It is a tree forty to fifty feet high; its branches are horizontally expanded, and the strobiles (cones) small and obovate. The young leafy twigs have a balsamic smell, and both they and the wood were formerly in great repute as a medicine; the oil obtained by distillation from the twigs, which has a pungent and camphor-like taste, has been recommended as a vermifuge. The wood of the stem is reddish, soft, and very light, but compact, tough, and durable, bearing exposure to the weather remarkably well. The tree is common in Great Britain, planted chiefly as an ornament. It seldom attains so great a size as in its native country. It flourishes in cool, moist localities. The Chinese arbor vitæ, Thuja orientalis, a native of China and Japan, which is immediately distinguishable from the former species by its upright branches and larger, almost globose and rough strobiles, is also, in Great Britain and upon the continent of Europe, a common ornament of pleasure grounds; but it does not attain so great a size as the preceding, and is more sensible of the cold of severe winters. The balsamic smell is very agreeable. The tree yields a resin with a pleasant odor, to which medicinal virtues were once ascribed; hence the name, arbor vitæ, given to this species and extended to the genus. There are several other species of Thuja, some of which seem well suited to the open air in the climate of Great Britain, and others require the protection of greenhouses. Among the former are Thuja plicata, California to Alaska, and Thuja dolabrata, a native of Japan, a tree of great height and thickness, which will not improbably prove one of the most important of the whole genus. In favorable forest conditions both Thuja occidentalis and Thuja plicata become rather large trees, the timber of which is very valuable. There are about sixty horticultural varieties of the American species, that vary in habit of growth, color of foliage, or other characteristics. Many of these are popular in landscape gardening. A tree common in North America and there known by the name of White Cedar is sometimes included in the genus Thuja, under the name of Thuja sphæroidea, but is more generally ranked in the genus Cupressus as Cupressus thyoides. See Cypress. Closely allied to the genus Thuja is Callitris. See Sandarac.

Fossil Forms. The genus Thuja, like many other forms of conifers, is represented by ancestral forms in Cretaceous rocks of northern Europe, and with the advance of time is found to migrate from northerly to more southerly regions, till during Pliocene time it disappeared from Europe. Thuja is also known in the Miocene beds of Dakota.