[Footnote 70: The bark is variable. Some trees of nearly 1 foot diameter have smooth green bark resembling that on young willow saplings; most others have the shaggy bark, while from some this has dropped away, exposing a smooth grayish interior suggesting that of the sycamore.] [Illustration: PLATE 27. PINE (_Pinus_). White Pine Foliage (_P. strobus_). Hard Pine Trunk (_P. palustris_). (_Photograph by Edward J. Davison_.) White Pine Tree (_P. strobus_). (_Courtesy N. C. Geol. Survey_.) Hard Pine Wood (_P. palustris_). Soft or Sugar Pine Wood (_P. lambertiana_).] NEEDLELEAF WOODS. The trees affording these woods cover large areas in the natural forests of the Northern Hemisphere. They exist, but to an unimportant extent, in the South. Cedar, larch, and cypress figure in ancient history, but woods generally were not employed until recent times.[71] Pine, spruce, hemlock, and other so-called soft woods are of this group. Needle-leaved woods are characterized by uniform fibre-conditions, presence of resins, and lighter weights. The vertical structure consists of simple, similar, elongated tubes or cells, tapering and finally closing at their ends, known as tracheids. These are arranged with more or less regularity, and woods are correspondingly easy to work. Pith-rays are scarcely visible, and sections do not show pores. Cavities known as resin-ducts, and which are not real vessels but rather simple intercellular spaces, secrete resins so important in making these woods durable and elastic. Trees afford large, straight pieces. Woods are used in carpentry and heavy constructions. The total requirement greatly exceeds that for hard woods. The resinous, usually evergreen, leaves and the cones are sufficient to identify these trees. Needleleaf, softwood, conifer, and evergreen trees are the same. [p130] FOOTNOTE [Footnote 71: See Oak, pages 11 _et seq._ The woods have always been important in the United States.] PINE. (_Pinus_.) These trees were not regarded seriously until about the latter half of the eighteenth century. Their woods are now the principal ones in carpentry and construction, and are more used than any others. They are to the soft woods what the oaks are to the hard woods, and they stand at present with reference to all woods much as iron does to all metals. Pine is prized because of a combination of strength, elasticity, light weight, working qualities, and availability, such as fits it for those constructions requiring the largest quantities of wood.