PLATE IV 



Crataegus douglasii (9a and 9b) 



Vessels present, diffuse in distribution with no particular 

 alinement; vessels relatively small and numerous; vessel 

 walls composed of five or six facets, giving the vessel a 

 definitely angular appearance; vessels grade into smaller 

 sizes as the growing season progresses without an abrupt 

 change in size; vessels solitary or in pairs, or in various 

 aggregates; vessel perforation plates simple; axial paren- 

 chyma absent or sparse, diffuse; rays one or two cells in 

 width (rarely three) . 



Holodiscus discolor (10a and 10b) 



Vessels present; vessels predominantly solitary or in pairs, 

 except for initial vessels which may be contiguous; growth 

 ring indistinct; vessels not changing in size or spacing from 

 early to late wood; vessels relatively few and far apart; per- 

 foration plates simple; rays three to many cells in width, 

 often massive, dispersed between uniseriate rays. 



