po s t e I 6 ia 163 



eighteen species occur in western America and 

 about the same number in eastern Asia. The 

 species may be grouped into several fairly dis- 

 tinct sections which are often recognized as 

 genera. The relationship of these sections is, 

 however, so complicated and the genera as cur- 

 rently recognized are so unsatisfactory that it 

 seems best to include them all under the genus 

 Abies. * 



Synopsis of American sections of Abies. 



A. Twigs roughened by the persistent leaf bases 

 (sterigmata), cone-scales persistent, longer 

 than the bracts. - 



a. Leaves sessile, quadrangular or flattened, 

 resin ducts of leaves lateral, cones axil- 

 lary or terminal. Picea 



b. Leaves with a single median resin duct, 



petioled, cones terminal, 

 aa. Leaves quadrangular, without pal- 

 isade tissue. Hesperopeiice 



bb. Leaves flat, with palisade tissue. 



Tsuga 



* See note on page 207. 



