WOOD. In all classes of plants, including for instance ferns, more highly organized than mosses, wood occurs in all members of the plant and is continuous from the finest rootlets up the root and stem, into the leaves and flowers or the equivalents of these. Wood performs two functions in the plant's life : first, it serves for the transport of water and contained salts, absorbed by the roots, to parts where this "raw sap" is needed and especially to the leaves; secondly it gives mechanical strength to the plant.
In palms and bamboos the wood of the leaves is string-like in form and is confined to the nerves or veins; from these the strings extend into the trunk or stem, where they descend but join one another at intervals thus producing a more or less basket-like or loose loofah-like complex, which is embedded in the general mass of tissue composing the rest of the trunk. Thus it is this linked
net-like complex of woody strings that corresponds to the solid mass of wood of a pine or oak.
Wood that has attained only slight thickness and accordingly cannot be termed timber, is nevertheless utilized, for instance in the form of thin branches and twigs to make besoms and baskets. Even when wood attains greater thickness it is not always timber since there are some woods so soft, light in weight, and weak that they have little or no value as structural material upon which there is a demand for strength: such wood supplies means of flotation for fishing-nets and buoys, and insulation, while the lightest of all are pith-like and are the materials of which sun-helmets are composed. (See also TIMBER.) (P. Gm.)