PLATE X 



Spiraea betulifolia (21a and 21b) 



Vessels present; vessels grade into smaller sizes as the 

 growing season progresses; without an abrupt change in 

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

 perforation plates simple; axial parenchyma absent; rays 

 one or two cells in width (rarely three). 



Philadelphus lewisii (22a and 22b) 



Vessels present; vessels predominantly solitary or in pairs, 

 except for initial vessels which may be contiguous; perfora- 

 tion plates scalariform; rays three to many cells in width, 

 often massive, dispersed between uniseriate rays; tracheids 

 and fibers alternating in radial bands . 



