Postelsia 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 
*k 
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. Hes pero peuce 
bb. Leaves flat, with palsade tissue. 
Tsuga 
* See note on page 207. 
