Most of the plants contained in this section are evergreen shrubs or low trees, but some of them attain a considerable size. Only one species, the deciduous Cypress, loses its leaves in winter. Many of the species are only half-hardy in Britain, and none of them are grown in this country for their timber. They all exude resin occasionally from their leaves and branches, but none of them produce turpentine. The catkins are but few flowered, and the cones are roundish. The leaves are frequently imbricated, at least when young; though in many of the species they vary considerably, even on the same tree. THE GENUS THUJA.—THE ARBOR VITÆ. [Illustration: FIG. 99.—YOUNG PLANT OF THE ARBOR VITÆ.] There are several species of this genus, but only two are common in British gardens. Of these the American Arbor Vitæ (_Thuja occidentalis_) is the largest tree; though it seldom grows above 30 feet high, and it is a great many years before it even attains that height. The male flowers and the female flowers are distinct, but on the same tree. The male catkins are small cones, with the pollen inclosed in four cases that are attached to the inside of the scale, near its base. The female catkins consist of six scales, with two ovules at the base of each; and the ripe cone has a sharp point projecting from each scale. The seeds have scarcely any wing; and when they germinate, they have only two cotyledons. The young plants send down a very long tap root (see _fig._ 99), and have some of their leaves imbricated and others loose. The Chinese Arbor Vitæ (_T. orientalis_) seldom reaches the height of 20 feet, but it may be also distinguished from the preceding species by its more dense habit of growth, by its branches being turned upwards instead of spreading horizontally, and by its leaves being smaller, closer together, and of a lighter green. THE GENUS CALLITRIS. Callitris is a genus separated from Thuja, of which only one species is as yet common in British shrubberies. This is the Gum Sandarach-tree, formerly called _Thuja articulata_, but now named _Callitris quadrivalvis_. The branches of this tree are articulated, that is, they may be broken off at the joints without lacerating the bark. The leaves are very small, quite flat, and articulated like the branches. The male catkins form a cone, in which the scales are disposed in four rows, with three or four anthers at the base of each. The female catkins are solitary, and they divide, when ripe, into four woody valves or scales, only two of which bear seeds. The seeds are small, and have a wing on one side. The tree is a native of Morocco and Barbary, in which countries it produces the gum-sandarach, which exudes like tears from every part of the plant. The wood is fragrant, very finely grained, and extremely durable, as is shown in the roof of the Cathedral of Cordova, built in the ninth century, which is of the wood of this tree. THE GENUS CUPRESSUS.—THE CYPRESS.