No law of growth governs the width of yearly rings, but circumstances have much to do with it. When the tree’s increase in size is rapid, rings are broad. An uncrowded tree in good soil and climate grows much faster than if circumstances are adverse. Carolina poplar and black willow sometimes have rings nearly three-fourths of an inch broad, while in the white bark pine, which grows above the snow line in California, the rings may be so narrow as to be invisible to the naked eye. There is no average width of yearly rings and no average age of trees. A few (very few) of the sequoias, or “big trees” of California, are two thousand years old. An age of six or seven centuries appears to be about the limit of the oldest of the other species in this country, though an authentic statement to that effect cannot be made. There are species whose life average scarcely exceeds that of men. The aspen generally falls before it is eighty; and fire cherry scarcely averages half of that. Of all the trees cut for lumber, perhaps not one in a hundred has passed the three century mark. That ratio would not hold if applied to the Pacific coast alone. _Spring and Summerwood_--These are not usual terms with lumbermen and woodworkers, but belong more to the engineer who thinks of physical properties of timber, particularly its strength. Yet, sawmill and factory men are well acquainted with the two kinds of wood, but they are likely to apply the term “grain” to the combination of the two. Spring and summerwood make the annual ring. Springwood grows early in the season, summerwood later. In fact, it usually is the contrast in color where the summerwood of one season abuts against the springwood of the next which makes the ring visible. The inside of the ring--that portion nearest the heart of the tree--is the springwood, the rest of the ring is the summerwood. The former is generally lighter in color. Sometimes, and with certain species, the springwood is much broader than the other. The summerwood may be a very narrow band, not much wider than a fine pencil mark, but its deeper color makes it quite distinct in most instances. In other instances, as with some of the oaks, the summerwood is the wider part of the annual ring. The figure or “grain” of southern yellow pine is largely due to the contrast between the dark summerwood and light springwood of the rings. The same is true of ash, chestnut, and of many other woods. _Pores_--Wood is not the solid substance it seems to be when seen in the mass. If magnified it appears filled with cavities, not unlike a piece of coral or honeycomb; but to the unaided eye only a few of the largest openings are visible, and in some woods like maple, none can be seen. The large openings are known as pores. They are so prominent in some of the oaks that in a clean cut end or cross section they look like pin holes. Very little magnifying is required to bring them out distinctly. A good reading glass is sufficient.