It is more difficult to trace the age of a hemlock limb than of many other kinds of trees, yet we can easily determine that many of the leaves are several years old when they fall. The bark of the hemlock is used in tanning hides for leather. The tree is much used for lumber. Where does it grow? THE ARBOR-VITÆ. One might almost wonder, at first sight, if the arbor-vitæ (often, but wrongly, called the white cedar) has any leaves at all. It does possess them, however, but they are very different in size and shape from any of the others that we have examined. They are small scale-like bodies, closely pressed together along the sides of the branchlets, in four rows. Leaves pressed to the branches in this manner are said to be "appressed." The leaves of the arbor-vitæ are so close together that they overlap one another. The leaves are of two distinct shapes, sometimes known as the surface leaves and the flank leaves. The former are located on what appears to be the flattened surface of the branchlets, while the latter are on the sides or edges. See Fig. 244. [Illustration: _Fig. 244. The Arbor-vitæ. Nearly full size._] If we carefully look at the leaves, we shall notice a raised spot near the point or tip. This is said to be a resin gland. This gland can be seen more plainly on the surface leaves that are two years old. Most of the leaves persist for at least two and sometimes three years; but even older ones can be found. These older leaves, however, exist not as green, active leaves, but merely as dried and lifeless scales. These lifeless leaves are probably detached from the branches by the forces of nature. The cones are even smaller than the hemlock cones. They are borne in the axils of the leaves in the same manner as the branchlets and are not conspicuous unless one is close to the tree. The arbor-vitæ is much planted for hedges and screens, as well as for other ornamental purposes. There are many horticultural varieties. The tree is abundant in a wild state in New York. SUMMARY OF THE KINDS OF COMMON EVERGREENS. _The white pine_ (Pinus Strobus).--Leaves in clusters of five, soft and slender; cones five or six inches long, slightly curved; bark smooth except on the trunks and larger limbs of old trees, where it is fissured. _The pitch pine_ (Pinus rigida).--Leaves in clusters of three, from three to four inches long, rather rigid; cones two to three inches long, often in clusters of two or more but frequently borne singly, persisting long after the seeds have been shed; bark more or less rough on the young growth and deeply fissured on the trunks of old trees. _The Scotch pine_ (Pinus sylvestris).--Leaves usually in clusters of two, from two to four inches long, rigid, of a bluish-green hue when seen in a large mass on the tree; cones two to three inches long and the scales tipped with a beak or prickle.