ANNUAL RINGS. 



15 



SPRING AND SUMMER WOOD. 



Examining the rings more closely, it is noticed that each ring is made 

 up of an inner, softer, light-colored, and an outer, or peripheral, firmer 

 and darker- colored portion. Being formed in the fore part of the sea- 

 son, the inner, light-colored part is termed spring wood, the outer, 

 darker portion being the summer wood of the ring. Since the latter is 

 very heavy and firm, it determines to a large extent the weight and 

 strength of the wood, and as its darker color influences the shade of 

 color of the entire piece of wood, this color effect becomes a valuable 

 aid in distinguishing heavy and strong from light and soft pine wood. 

 In most hard pines, like the longleaf, the dark summer wood appears 

 as a distinct band, so that the 

 yearly ring is composed of two 

 sharply defined bands — an inner, 

 the spring wood, and an outer, 

 the summer wood. But in some 

 cases, even in hard pines, and 

 normally in the wood of white 

 pines, the spring wood passes 

 gradually into the darker sum- 

 mer wood, so that a sharply de- 

 fined line occurs only where the 

 spring wood of one ring abuts 

 against the summer wood of its 

 neighbor. It is this clearly 

 defined line which enables the 

 eye to distinguish even the very 

 narrow rings in old pines and 

 spruces. In some cases, espe- 

 cially in the trunks of Southern 

 pines, and normally on the lower 

 side of pine limbs, there occur 

 dark bands of wood in the spring wood portion of the ring, giving rise 

 to false rings which mislead in a superficial counting of rings. In the 

 disks cut from limbs these dark bands often occupy the greater part of 

 the ring and appear as "limes" or sickle-shaped figures. The wood 

 of these dark bands is similar to that of the true summer wood — the 

 cells have thick walls, but usually lack the compressed or flattened 

 form. 



Normally, the summer wood forms a greater proportion of the ring 

 in the part of the tree formed during the period of thriftiest growth. 

 In an old tree this proportion is very small in the first 2 to 5 rings 

 about the pith, and also in the part next to the bark, the intermediate 

 part showing a greater proportion of summer wood. It is also greatest 

 in a disk taken from near the stump and decreases upward in the stem, 



srir spur 



Fig. 3. — Board of pine. OS, cross section ; BS, radial 

 section ; TS, tangential section ; sw, summer wood ; 

 spiv, spring wood. 



