clusters of a few cells in the early wood progressing to 

 radial files which are grouped secondarily to form tan- 

 gential bands in the late wood „ Rhus glabra (p. 52-53) 



31 Axial parenchyma distributed as an occasional single 

 cell adjacent to a vessel; vessels diffuse, not grouped 



as above . . . Pachistima myrsinites (p. 64-65) 



32 Axial parenchyma predominantly terminal 33 



32 Axial parenchyma predominantly diffuse or absent . . . . . . . . 35 



33 Vessels decreasing gradually in size from early to late 

 wood; vessels smooth in outline, solitary or in occasional 



pairs . . . . . . . o Physocarpus malvaceus (p. 16-17) 



33 Vessels not decreasing gradually in size as above; vessels angular in outbne 34 



34 Vessels arranged in diagonal and/or radial Lines . Rhamnus alnifolia (p. 56-57) 



34 Vessels solitary or in occasional multiples of a 



few cells . . . o Rhamnus purshiana (p. 56-57) 



35 Vessels occurring in patterns of radially alined S curves 



in mature wood; tannins occurring in even the young ray 



parenchyma. ......... Ceanothus spp. (p. 54-55) 



35 Vessels not in patterns as described above; tannins, if present, occurring in ray 



parenchyma only in the more mature cells 36 



36 Axial parenchyma numerous 37 



36 Axial parenchyma absent or sparse 39 



37 Vessel walls composed of five or six facets, giving the vessel a definitely angular 



appearance ............. . ... 38 



37 Vessel walls, although composed of several facets, giving 



a smoother, more rounded outline than above. .... Amelanchier alnifolia (p. 12-13) 



38 Vessels tending to form concentric bands within the 



growth ring; vessels relatively few and large . . . Shepherdia canadensis (p. 64-65) 



38 Vessels diffuse in distribution with no particular 



alinement; vessels relatively small and numerous. Crataegus douglasii (p. 14-15) 

 39 Spring wood vessels large, numerous, and solitary 



(although closely spaced); vessels of late wood not 



greatly smaller than those of early wood, but much 



more widely spaced; vessels markedly angular, with 



concave facets Sorbus scopulina (p. 24-25) 



39 Spring wood vessels not as above;" if vessel spacing is as above, then vessels are 



rounded, with convex facets; if vessel shape is as above, then spacing differs .... 40 

 40 Early wood with a few large vessels; vessel size 

 decreases greatly from early to late wood, but 



spacing of vessels remains similar Cercocarpus ledifolius (p. 12-13) 



40 Early wood may have a few large vessels but, if so, then the vessel size and 



spacing differ from the above 41 



41 Axial parenchyma absent . ............. Spiraea betulifolia (p. 26-27) 



41 Axial parenchyma present although few in number. 42 



42 Vessels angular in outline 43 



42 Vessels rounded in outline ........... Purshia tridentata (p. 18-19) 



43 Ray cells squared in outline in cross section ..... Lonicera utahensis (p. 58-59) 



43 Ray cells radially elongated in cross sections .... Lonicera involucrata (p. 58- 59) 



6 



