TECHNICAL QUALITIES OF THE TREES 



101 



lignin, tannin, &c., in the walls of cells formed a number of years before. The number of years elapsing 

 before incrustation takes place is small in catalpa, chestnut, locust; and larger in yellow poplar, white oak, 

 walnut where it comprises about thirty or forty rings. Beech, maple, basswood, &c. do not form any 

 heartwood proper. A darker coloring of the inner layers indicates, in the cases of these species, the 

 beginning of a decomposition rather than an incrustation. 



HARDWOODS. 



(') Sapwood frequently very thick. 



(■) Heartwood indistinct and not recognized as such by lumbermen. 



(') Heartwood not distinct. 



(*) Rays more distinct than other members of this group. 



(=) Rays less distinct than other members of this group. 



(') Rays very conspicuous on radial section. Cornus florida sometimes has heartwood. 



