96 ECONOMIC WOODS OF THE UNITED STATES 



of 2-5; tyloses present. Color brown or purplish; 

 never yellow. Rays fine, scarcely visible to un- 

 aided eye; 1—1 seriate, few to 30 cells high; mostly homo- 

 geneous. Pits between vessels and ray cells mostly simple. 

 Growth rings terminated by narrow band of very thick- 

 walled, flattened wood fibres. Walnut. 45 



a 4 Wood rather dense; sp. gr., .60-70. Odor mild 

 but characteristic. Color rich dark or chocolate- 

 brown or purplish; sometimes variegated. Sap- 

 wood usually rather wide. Wood parenchyma with 

 abundant crystals. Ray cells circular (tangential section). 

 Black Walnut, Juglans nigra L. (C, A) (Plate 

 IV, Fig. 6); California Walnut, J. calif ornica 

 Wats. (Ps).* 



b 4 Wood light and soft; sp. gr. .35-45. Odorless. 

 Color light chestnut brown with darker zones. 

 Sapwood very thin. Crystals absent. Ray cells 

 small and compressed laterally. Butternut, White 

 Walnut, J. cinerea L. (C, N). 



b 3 Wood parenchyma about pores and, in late wood, 

 joining groups of pores into irregular tangential 

 lines. Pores irregularly disposed; solitary or in 

 short radial groups. Tyloses absent. Color yel- 

 low. Wood dense; sp. gr. .60-70. Rays fine, 1-6, 

 mostly 3-4, cells wide and few to 40 cells high; mostly 

 heterogeneous. Pits between vessels and ray cells half- 

 bordered. Terminal fibres flattened but not thicker-walled 

 than others. Yellow-wood, Cladrastis lutea (Michx. 

 f.) Koch. (Sc). 



b 2 Pores of approximately same size throughout growth 

 ring; no tendency to become ring-porous. Growth 

 rings not always distinct. 



a 3 Wood parenchyma in tangential lines. "Ripple 

 marks" present or absent. Pores resinous or 



gummy. 



* In the Yale collection is a board of Juglans cnlif ornica in which the late 

 wood is much lighter in color and the fibres much thinner-walled than in early 

 wood. 



