16 Vessels forming a zigzag pattern, radially alined . Ribes viscosissimum (p. 34-35) 

 16 Vessels may be diagonally alined, in short 



tangential bands, and/or diffuse, with none of 



these found exclusively; there is not the regularity 



of alternating diagonal bands as in the above .... Ribes irriguum (p. 30-31, 34-35) 



or Ribes setosum (p. 32-33) 



17 Vessels commonly in radial multiples; often spring 



wood vessels are closely spaced singles or in irregular 

 clusters (some appearing as subdivisions of a single 

 vessel), the vessels progressing toward formation of 



radial multiples from early to late wood 18 



17 Vessels solitary, in pairs, or in various aggregates, including sometimes radial 



vessel chains but not vessel multiples 24 



18 Perforation plates simple .19 



18 Perforation plates scalariform . 22 



19 Rays composed of procumbent cells only . «... 20 



19 Rays composed of both procumbent and upright cells , 21 



20 Vessels with spiral thickenings; rays mainly 



uniseriate but some 2 to 4 cells wide Acer glabrum (p. 36-37) 



20 Vessels without spiral thickenings; rays 



uniseriate only . . . . Populus spp. (p. 38-39, 40-41) 



21 Rays 1 cell in width . . . Salix scouleriana (p. 40-41) 



21 Rays 2 to 4 cells in width Sambucus spp. (p. 60-61, 62-63) 



22 Rays uniseriate only. 23 



22 Rays both 1 and 2 cells in width Betula spp. (p. 44-45) 



23 Axial parenchyma forming tangential bands at short 



intervals between rays Alnus incana (p. 42-43) 



23 Axial parenchyma sparse and diffuse Alnus sinuata (p. 42-43, 46-47) 



24 Vessel perforation plates scalariform 25 



24 Vessel perforation plates simple 28 



25 Vessels regular in size and spacing throughout 



growth ring Cornus stolonifera (p. 46-47) 



25 Vessels not regular in size or spacing as above 26 



26 Rays 1 to several cells wide Vaccinium spp. (p. 50-51, 52-53) 



26 Rays uniseriate only. . 27 



27 Growth ring initiated by a single row of large, 



closely spaced vessels. . Menziesia ferruginea (p. 50-51) 



27 Growth ring not initiated as above; no clear line 



of large vessels Ledum glandulosa (p. 48-49) 



28 Annual ring initiated by a definite band of large vessels; other vessels are much 

 smaller and sparse, giving a two-banded appearance to the growth ring 29 



28 Annual ring not initiated by band of large vessels as above; vessels grade into 



smaller sizes as the growing season progresses without an abrupt change in size . . 30 



29 Axial parenchyma numerous, paratracheal, and diffuse, 



often encircling the larger vessels Symphoricarpos albus (p. 62-63) 



29 Axial parenchyma few, if in contact with a vessel, a 



single cell rather than an encircling band . Arctostaphylos uva-ursi (p. 48-49) 



30 Axial parenchyma predominantly paratracheal 31 



30 Axial parenchyma predominantly terminal or diffuse 32 



31 Axial parenchyma distributed as 2 to several cells on the 

 periphery of each vessel group; vessels solitary or in 



5 



