"As the tree grows from the outside," said Mr. Wilson, "the older part of the stem is subject to more and more pressure. The walls of soft matter between the wedges of wood become thinner and thinner, till they are the finest sheets, and the medullary tissue itself has ceased to be living matter. After this it no longer carries up the sap. When the stem is cut across, only the thin edges of these partition walls are seen, and they appear to be mere lines." "Thank you, sir," said Fred. "These are the lines then that the cabinet-maker calls the silver-grain of the wood.""Yes, Fred, they are," said Mr. Wilson. "The beauty ofthe wood depends upon the closeness of its texture, and the skill of the workman in cutting it so as to expose this silver grain. Which part of the woody stem did you say was first formed?""The central part of the stem, sir, is the oldest wood in the tree.""Tell me again what happens to this part as new layers are formed one by one around it?""The outer layers press upon it more and more, sir, and it becomes denser and denser.""Quite true," said Mr. Wilson, "and it becomes the hardest wood in the tree. It is called heartwood. Heart- wood is always selected where strength and durability are required. The heartwood becomes darker and moredeeply coloured than the layers round it, and it is the graduation of coloring that makes our cabinet woods so beautiful.
