14 ECONOMIC WOODS OF THE UNITED STATES 



Stone, H.: The I'so of Anatomical Characters in the Identification of Wood, 



Nature, Vol. LXV, No. 1686, 1902, pp. 379-380. 

 Gayer, K. : Schlich's Manual of Forestry, Vol. V, 1908, pp. 7-19. 

 Metzger, K. : Ueber der Konstructionsprinzip des secundiiren Holzkorpers, 



Naturw. Zeitschrift fiir Forst- und Landwirtschaft, 6. Jahrgang, 



1908, pp. 249-273. 

 WiELER, A.: Ueber die Bcziehung zwischen Wurzel-und Staumholz, Forstw. 



Jahrbuch, Tharand, Vol. XLI, 1891, pp. 143-171. 

 Hartig, Robert: Untersuchungcn iiber die Entstehung und die Eigenschaf- 



ten des Eichenholzes, Forstlich-naturw. Zeitschrift, Vol. Ill, 1894, pp. 



1-13; 49-68; 172-191; 193-203. 

 Hartig, Robert, and Weber, Rudolph: Das Holz der Rothbuche in Ana- 



tomisch-physiologischer, Chemischer und Forstlicher Richtung, Berlin, 



1888, pp. 20-28. 

 Sanio, Carl: Vergleichende Untersuchungen iiber die Elementarorgane des 



Holzkorpers, Botanische Zeitung, Vol. XXI, 1863, pp. 85-128. 

 : Verg. Unt. u. d. Zusammensetzung des Holzkorpers, Ibid., Vol. 



XXI, 1863, pp. 358-412. 

 Wiesner, Julius: Die Rohstoffe des Pflanzen Reiches, Vol. II, Leipzig, 1903, 



pp. 1-35. 



VESSELS (see Appendix, p. 132) 



Vessels are indeterminate, tube-like cell-fusions found in the 

 wood of all indigenous dicotyledonous plants. In fact the absence 

 of xylem vessels in woody Dicotyledons is a very rare phenomenon 

 which, according to Solereder {loc. cit., p. 1136), has been recorded 

 only in the exotic genera Drimys and Zygogynum of the Mag- 

 noliaceoB, and Tetracentron and Trochodendron of the Trochoden- 

 draceoe. 



Vessels arise from cambial cells which increase in size and, 

 through the partial or complete absorption of their end-walls at 

 the close of the process of thickening, become continuous, in a 

 longitudinal row. There is always a constriction at the place of 

 fusion of the cells, thus plainly demarking the vessel segments (Plate 

 VI, Nos. 3, 4, 6). The walls of contact of the segments of a ves- 

 sel are sometimes (a) horizontal, but more often (6) oblique, and 

 fit together exactly; or, again, they may be (c) oblique with a por- 

 tion of the opposed faces united, the pointed and blind ends extend- 

 ing beyond the division wall, as in Liquidamhar and Qucrcus. In 

 (a) the perforation from one segment to another is simple, i.e., with 

 one round opening. In (6) and (c) the perforations are sometimes 



