32 The Farm Woodlot 



may be quite plainly seen. In the center is a small spot of 

 pith varying from a mere pin point in the pine to a half 

 inch in diameter in some of the sumacs and elders. This 

 was the original live tissue from which the rest has grown. 

 Surrounding it are a number of concentric rings, very 

 distinct in the oak, almost invisible in the black gum. 

 Each ring represents the growth of a year. The inner 

 portion of the ring is usually of a lighter color and softer 

 texture. This is the spring wood. It is formed in the 

 spring when the tree is living on the food stored over from 

 the preceding season, and the walls of the cells, of which all 

 wood is composed, are very thin. The wood of deciduous 

 trees, the hardwoods, is usually full of little holes, the 

 cross-sections of hollow cells ; in the conifers, or softwoods, 

 the holes are so small that they cannot be seen with the 

 naked eye. The outer portion of the ring is of darker 

 color and harder tissue. This is the growth of the summer 

 or autumn, when the leaves are furnishing an abundance 

 of food, and the cell walls are very thick. The contrast 

 is very much stronger in some woods than in others. 

 In the tropical forests, the trees either do not show these 

 rings at all, or, when present, they do not represent years 

 of growth. There the growth is continuous throughout 

 the year, except when interrupted by drought ; there is no 

 cold weather to bring about a rest period. Consequently 

 rings, when present, represent periods of drought instead 

 of years, and the age of the trees cannot be ascertained 

 definitely in this way. If the trunk examined is an oak, 

 there will be evident streaks of white wood radiating from 

 the central pith, like the spokes of a wheel, only in broken 

 lines. These are called the pith rays or medullary rays. 



