THE TIMBERS OF COMMERCE 



Authorities. Schwartz (106), p. 483. Hartig (42). Laslett 

 (60), p. 146. Martin (68), p. 240. Nordlinger (87), p. 523. 

 Ditto (86), vol. iii. p. 53. Mathieu (69), p. 310. Gamble (37), 

 p. 392. Watt (127). Wiesner (113), L. 12, p. 833. 



Colour. Dark brown, walnut to black heart-wood. Sap- 

 wood yellowish, brownish, or dirty white. 



Anatomical Characters. Transverse section : 



Pores. Readily visible from their size : grade 2 : somewhat 

 variable, increasing in size as the tree ages : evenly distributed : 

 few from 3-13 per sq. mm. : in most rings a distinct though loose 

 pore-ring of 2-3 rows of pores : many subdivided groups of 2-5 

 pores in compact, radial groups. 



Rays. Need lens, size 3-4, medium, uniform : straight, rarely 

 avoiding the pores : rather short : much denser than the ground- 

 tissue throughout the ring : numerous, 7-9 per mm. : tapering 

 gradually : a pore- width or less apart. - 



Rings. Clear but not striking : obscure in the solid wood in 

 dark specimens : boundary a fine line of wood scarcely wider 

 than the rays : gently undulating. 



Soft-tissue. In excessively fine lines, concentric and more or 

 less continuous, very numerous and close : a much more pro- 

 minent feature than in J. nigra : visible by reflected light only : 

 also encircling the pores. 



Pith. Cavity 2-5 mm. wide : round or lobed : contains a 

 series of thin, flinty diaphragms. 



Radial Section. Considerably lighter in shade than the Trans- 

 verse : never purplish. Pores, open grooves, mostly black and 

 shining. Rays, visible in certain rights, clear but not prominent. 

 Ring-boundary line traceable with lens. Soft-tissue excessively 

 fine, close, parallel lines (lens). 



Tangential Section. As the Radial, but the boundary-line trace- 

 able by its lustre and by the fringes of the loops. Rays fine 

 brown lines (lens), about 0*5 mm. high. 



Type specimens from commercial sources and from trees known 

 before felling. 



No. 184. AMERICAN WALNUT. Juglans nigra. 



Linn. 



PLATE XIII. FIG. 116. 

 Natural Order. Juglandaceae. 

 The J. nigra of Thunberg is J. Sieboldiana, Max. 

 Sources of Supply. North America, United States and Canada. 

 Alternative Names. Black Walnut : Waney Black Walnut. 

 Physical Characters, etc. Recorded dry- weight 30-55 Ibs. per 

 cu. ft. Hardness Grade 6, firm, compare Chestnut, Beech or 



210 



