ECONOMIC WOODS OF THE UNITED STATES 95 



somewhat heterogeneous. (Plate IV, Fig. 3.) Vessels without 

 spirals; perforations simple; pits into ray cells simple or half- 

 bordered. Hickory.* 44 



a 3 Wood very hard, heavy (sp. gr. .80-85), tough, 

 strong, resilient. Wood fibres normally very thick- 

 walled.f Shagbark, Hicoria ovata Brit. (C, N) 

 (Plate IV, Fig. 3) ; Big Shellbark, H. laciniosa Sarg. 

 (C); Mocker Nut, H. alba Brit. (C, N, S); Pignut, 

 H. glabra Brit. (C, N, S). 



b 3 Wood hard, heavy (sp. gr. .70-.75), brittle, fairly 

 strong. Wood fibres comparatively thin-walled. Pecan 

 H. pecan Brit. (S, C) ; Nutmeg Hickory, H. myris- 

 ticceformis Brit. (S); Bitternut, H. minima Brit. 

 (C, N, S); Water Hickory, H. aquatica Brit. (S).J 



B DIFFUSE-POROUS WOODS. Pores fairly uniform in size and dis- 

 tribution throughout growth ring; occasionally more numerous 

 and very often somewhat larger in early wood, but without 

 forming a distinct ring or band. 



a Pores variable from large to small, all or at least a portion 

 of them readily visible to the unaided eye; comparatively 

 few to numerous. Large vessels very distinct on longi- 

 tudinal surface. Woods (except Juglans cinerea) moder- 

 ately to extremely dense. (For b, see p. 99.) 



a 1 All rays fine. Pores not in continuous radial lines. 

 (For b 1 , see p. 98.) 



a 2 Pores comparatively large in early wood, diminishing 

 in size toward outer margin of growth ring; some- 

 times approaching ring-porous. Growth rings dis- 

 tinct. Vessels without spirals; perforations simple. 



a 3 Wood parenchyma in numerous very fine concen- 

 tric lines, independent of pores. Pores often in 

 echelon arrangement; solitary or in radial groups 



* Specific distinction within the two groups of hickory woods is ordinarily 

 not possible. The commercial names "red hickory" and "white hickory" 

 refer to heartwood and sapwood, respectively. By "second-growth hickory" 

 is meant wide-ringed wood and particularly the sapwood. 



t Occasional exceptions to this general rule have been noted. 



j Hicoria aquatica is so nearly diffuse-porous that it can usually be dis- 

 tinguished from the other species. 



