NOTES ON THE STRUCTURE OF THE WOOD OF THE FIVE SOUTHERN PINES. 



(Pinus i^alustris, hcterophijJla, echinata, Utila, ijiahra.) 



By FiLIBEKT RoTii, 

 In charge of Timber Phydes, Division of Foreatry, 



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. Uere it is proposed to give in more detail the char- 

 acteristics of the wood structure. 



SAr AND HEART WOOD. 



All five species have a distinct sap and heartwood, 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. 



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

 of rings involved in either and also in the age at which the transition from sap to heartwood 

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

 in young trees wlien 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 tree 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 Lougleaf Pine (No. 22) was, for 

 instance, found to show the following relations: 



The change from sax> to heart wood begins earlier in young trees than in the younger portions 

 of older trees; in these latter, sections thirty-six and forty years old are quite commonly found 

 still entirely made up of sapwood, while in young trees, as stated above, the change begins before 

 the age of thirty years. 



The progress of the transformation is somewhat influenced by the rate of growth; it is slower 

 in slow-growing trees and usually also on the slower-growing radius, i. e., there are more rings of 



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