98 DUDLEY MEMORIAL VOLUME 



4. Pseudotsuga. 



Large evergreen forest trees, with flat, indistinctly 2-ranked leaves, nar- 

 rowed at base into short petiole; leaf-scars sessile. Cones pendent, their 

 3-pronged bracts much exserted ; seeds prominently winged. 



A genus of three species; two in western America, and one in Japan. 



1. Pseudotsuga taxifolia Britton. Douglas Fir. 



Leaves ^-\ l /2 inches long, obtuse, dark green above, paler beneath; 

 cones oblong-ovate, 2-4 inches long, light reddish brown, with broad, rounded 

 scales and well exserted 3-parted bracts. 



The Douglas Fir is the most important timber tree of western America. 

 It often attains a height of 200 feet or even more, and a trunk 12 feet in 

 diameter. Frequently planted in the Arboretum. Native trees are growing 

 on the Palo Alto estate at the north end of Jasper Ridge. 



5. Abies. Firs. 



Trees generally pyramidal in outline, with their branches in whorls. 

 Leaves solitary, scattered along the twigs in definite spirals, but often appear- 

 ing 2-ranked by a twist near the base, linear, flat or slightly 4-sided, some- 

 times narrowed at base but not into a distinct leaf-stalk; leaf -scars sessile on 

 the smooth twigs. Cones erect on the branches, their scales deciduous, and 

 bracts exserted beyond scales or concealed by them. 



A genus of 24 known species, which inhabit the northern or mountainous 

 parts of the northern hemisphere. 

 Leaves stomatiferous and alike in color on both surfaces. 



Leaves rigid, spreading from all sides, Ys'Y* inch long, closely crowded on 

 the twigs, their much enlarged bases nearly contiguous. 



Leaves Ys'Y* inch long, steel green, 1/12 inch wide, somewhat 4-angled. 



1. A. pinsApo. 

 Leaves Y*~ 2 A mcn l n g> dark green, Y% inch wide. 



2. A. barborensis. 

 Leaves curved upward on twigs, more or less 2-ranked, pale glaucous 



green, 1-2 inches long. 3. A. concolor. 



Leaves stomatiferous only on lower surface. 



Leaves bright green on lower surface, distinctly 2-ranked. 



4. A. Momi. 



Leaves silvery on lower surface with 2 broad bands of stomata. 

 Leaves not pungently acute. 

 Leaves obtuse. 



Leaves distinctly 2-ranked, forming flat sprays; twigs ill-scented 

 when bruised. -5. A. grandis. 



