PLATE XVI 



Populus tremuloides (31a and 31b) and 



Populus trichocarpa (32a and 32b) 



Vessels present; vessels commonly in radial multiples; often 

 spring wood vessels are closely spaced singles or in irregu- 

 lar clusters (some appearing as subdivisions of a single vessel) , 

 the vessels progressing toward formation of radial multiples 

 from early to late wood; vessels without spiral thickenings; 

 perforation plates simple; rays composed of procumbent cells 

 only; rays uniseriate only. 



