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) cambiimi, 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-fascicular 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 



DeBaht, 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, Jime 1911. 



RuBNBK, Konbad: Das Hungem des Cambiums und das Aussetzen der 

 Jahrringe, Naturw. Zeitschrift f iir 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. Hot. 

 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 



