PLATE 2. EXOGENOUS STRUCTURE IN WOOD.
Yearly Rings or Layers.
A section of a Longleaf Pine Tree.
A section of Oak showing "porous" structure in yearly layers. (Natural size.)
A section of Hard Pine showing "solid" structure in layers. (Natural size.)
EXOGENOUS TREES. (Dicotyledons.)
Exogenous trees are those the trunks of which are built up by rings or layers, each deposited consecutively upon the outside of the others. A section exhibits first a central point or canal known as a pith-cavity, next and consecutively the annual layers, and finally the bark. The woods of this series are familiar to all. The oaks, pines, and practically all of the merchantable lumbers are among them. The forests are widely distributed, and the species are so numerous as to present an almost infinite range of possibilities.
Fig. 2.—Section Boxelder, showing Pith-cavity at Centre.