14 ECONOMIC "WOODS OF THE UNITED STATES 



Stone, H. : The Use of Anatomical Characters in the Identification of Wood, 



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

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

 Mbtzger, K. : Ueber der Konstruetionsprinzip des secundaren Holzkorpers, 

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

 1908, pp. 249-273. 

 Wieler, a. : Ueber die Beziehung zwischen Wurzel- und Staumholz, Forstw. 

 Jahi-buch, Tharand, Vol. XLI, 1891, pp. 143-171. 

 . / Hartig, Robert: 'Untersuchungen uber 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, Chemiseher und Forstlicher Richtung, Berlin, 

 1888, pp. 20-28. 



Sanio, Carl: Vergleichende Untersuchungen uber die Elementarorgane des 

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



: Verg. Unt. ii. d. Zusammensetzung des Holzkorpers, IHd., Vol. 



XXI, 1863, pp. 358-412. 



WiESNER, JuLiTJs: Die Rohstoffe des Pflanzen Reiches, Vol. II, Leipzig, 1903, 

 pp. 1-35. 



VESSELS 



Vessels are indeterminate, tube-like elements present 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- 

 noliacece, and Tetracentron and Trochodendron of the Trochoden- 

 draceos. 



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 (b) 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 Liqmdcmhar and Quercus. In 

 (a) the perforation from one segment''{;o anOT^ePis simple, i.e., with 

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



