12 ECONOMIC WOODS OF THE UNITED STATES 



CAMBIUM 



As previously stated, that portion of a pro-cambium strand 

 which remains capable of division and generation is known as 

 fascicular (i.e., bundle) cambium, since it produces on the inner 

 side wood or xylem, and on the outer phloem collectively a fibro- 

 vascular bundle. The cambia of the several bundles are later 

 united into a continuous sheath, and the portion between the 

 original bundles is termed the inter-fasdcular cambium. The 

 cambial layer sheathes the entire woody cylinder from root to 

 branch and separates it from the cortex or bark. It is composed 

 of a thin layer of delicate, thin-walled, vertically elongated cells 

 filled with protoplasm and plant food. It is this layer that is 

 torn when bark is stripped from a living tree. During vigorous 

 growth, "when the sap is up," the cells of the cambium are par- 

 ticularly delicate, a fact taken advantage of in peeling poles, logs, 

 and basket-willow rods. 



The division and development of the cambial cells give rise 

 to (a) a layer of new wood on the outside of that last produced; 

 (6) a layer of new phloem on the inside of that last produced; (c) 

 continuation of the medullary rays of both xylem and phloem; 

 and (d) new cambium. 



References 



DEBARY, A.: Comparative Anatomy, pp. 454-475. 



BAILEY, I. W.: Relation of Leaf-Trace to Compound Rays in Lower Dicoty- 

 ledons, Annals of Botany, Vol. XXV, No. 97, June 1911. 



RUBNER, KONRAD: Das Hungern des Cambiums und das Aussetzen der 

 Jahrrrnge, Naturw. Zeitschrift fur Forst- und Landwirtschaft, 8. Jahr- 

 gang, 1910, pp. 212-262. 



VON MOHL, HUGO: Ueber die Cambiumschicht des Stammes der Phanero- 

 gamen und ihr Verhaltniss zum Dickenwachsthum desselben, Bot. 

 Zeitung, Vol. XVI, 1858, pp. 183-198. 



SECONDARY WOOD 



Tissues formed from cambium are termed secondary. Almost 

 all of the wood of a stem is secondary wood, the small amount of 

 primary wood being wholly negligible from a technological point of 

 view. 



The principal functions of secondary wood are (a) to provide 



