106 



FORESTRY INVESTIGATIONS U. S. DEPARTMENT OF AGRICULTURE. 



2. Pith lays not or larely broader than the pores, fine but conspicuous 



a. Wood heavy and hard, usually of darter i eddish coloi and commonly spotted on cross section.. Bed maple. 



b. Wood of medium weight and hardness, usually light colored Silver maple. 



Red maple is not always safely distinguished from soft maple. In box elder the pores are finer and more 



numerous than in soft maple 



The various species of elm may be distinguished as follows: 



1. Poies of spring wood form a bioad baud of several rows; easy splitting, dark biown heart Med elm. 



2. Pores of spring wood usually m a single row, or nearly so. 



a. Pores ol spring wood large, conspicuously so White elm. 



b. Pores of spring wood small to minute. 



a'. Lines of pores in summer wood fine, not as wide as the intermediate spaces, giving rise to very 



compact gram BocJc elm. 



V. Lines of pores broad, commonly as wide as the intermediate spaces Winged elm. 



c. Pores in spi mg wood indistinct, and therefore haidly a ring-porous wood Cedar elm. 



su^v: 



>sp.w. 



Fig V) —"Wood of wain at p r, pith rays 

 e Z, conccntriclmcs, v, Teasels or ports, 

 i (/ w , summer wood sp w , spring wood 



FIG 16 Wood of cherry. 



STRUCTURE OF THE WOOD OF THE FIVE SOUTHERN PINES. 1 



The wood of these pines is so much alike in appearance and even in minute structure that 

 it can be discussed largely without distinction of species. The distinctions, as far as there are 

 any, have been pointed out in the introduction. Here it is proposed to give in more detail the 

 characteristic s of the wood structure. 



SAP AND HEART WOOD. 



All five species have a distinct sap and heart wood, the sap being light yellow to whitish, the 

 heart yellowish to reddish or orange brown. The line of demarcation between the two is well 

 defined, without any visible transition stage. The location of this line does not as a rule coincide 

 with the line of any annual ring, so that the wood of the same year's growth may be sap on one 

 side of the tree and heart on the other. The difference in this condition may amount to ten or 

 twenty rings, which on one side of the same section will be heart, on the other side sap. 



Theie is considerable variation in the relative width of the two zones as well as the number 

 of rings involved m either and also in the age at which the transition from sap to heart-wood 

 begins. This age was rarely found to be below twenty years; as a rule the transformation begins 

 in young trees when the particular section of the tree is between twenty and twenty-five years 

 old, but the progress of heart formation does not keep pace with the annual growth, being more 

 and more retarded as the tiee grows older, so that while in a section twenty-five years old twenty- 

 two rings may be sap wood, at thirty-five years the sapwood will comprise only thirty rings; at 

 forty- five years, forty rings; at eighty years, fifty rings; and in sections two hundred years old 

 the outer eighty to one hundred rings will still be sap. A young tree of longleaf pine (No. 22) 

 was, foi instance, found to show the following relations: 



Section 



Height 



from 



stump 



Age of 

 section 



1 

 Kings o± | 

 sap 



III 



IV 



VII 



JL J\. - • i 



XII 



Feet 

 6 



22 

 30 

 42 



Year? 

 46 

 $8 

 30 



18 



Number 



40 1 



as 



27 

 23 

 17 



.Reprinted from Bulletin 13, 



