208 MISC. PUBLICATION 303, U. S. DEPT. OF AGRICULTURE 
Pseudotsuga douglasii, see Pseudotsuga taxifoUa. 
Pseudotsiiga glauca Mayr.^ Colorado Douglas fir. 
P. douglasii glauca Mayr. 
Range : 9, 11, 13, 14, 16. 
Site : Well-drained, snn. 
Fruit : Cone, available September-October. 
A large evergreen tree ; resistant to winter cold ; susceptible to spring frost ; 
grows well on dry, sandy soil and moist loamy soil but not clay, gravel or poorly 
drained sites ; slow growing ; wood much less valuable commercially than that 
of P. taxifoUa; does not pioneer in burns; shorter lived than P. faxifQlia. 
Stomach records: Richardson's grouse; plains white-tailed deer, black-tailed 
deer, mountain sheep. Ohservations: Captive sharp-tailed grouse, dusky grouse; 
red squirrel, chestnut-mantled ground squirrel, porcupine, bighorn. 
Pseudotsuga macrocarpa (Torr.) Mayr. Eigcoae spruce. 
Range: 4, 5, 10. 
Site: Dry, weU-drained, sun. 
Fruit: Cone; mature in August, seeds shed August-September, some 
cones persistent the year round. 
A large evergreen tree; slow growing; wood not used commercially; seed 
vitality low but persistent. 
O'bso'vations: Seeds eaten by rodents and birds. 
Pseudotsuga muerouata, see Pseudotsuga tawifoJm. 
Pseudotsuga taxifoUa (Lam.) Britt. Oregon Douglas fir. 
P. douglasii Carr., P. mucronata (Raf.) Sudw., P. douglasii caesia Schwerin. 
Range : 1, 2, 3, 4, 5, 6. 
Site : Well-drained, sun. 
Fruit: Cone; mature September-October, seeds shed at once. 
A very large evergreen tree ; demands high relative humidity for best growth ; 
cannot withstand severe cold or drying winds; grows best on well-drained, 
sandy loam; absent from poorly drained areas; growth rate rapid; an ex- 
tremely important timber tree; often a pioneer in burns; much larger and 
longer lived tree than P. glauca. (See footnote under P. glauca.) 
Var. caesia Schwerin is a form more or less intermediate between this species 
and P. glauca; it occurs in regions 6, 7, and 12; makes no summer growth and 
is slower growing than the species. 
Observations: Dusky and Franklin grouse; browsed as a last resort by Olym- 
pic wapiti; porcupine; much eaten by Douglas squirrel, Sierra chickaree, red 
spruce squirrel, and Magdalena chipmunk ; of slight importance as browse for 
mule deer. 
Psiiostrophe cooperi (Gray) Greene. 
Riddelia cooperi Gray. 
Range: 9, 10, 11. 
Site : Dry, well-drained, sun. 
Fruit : Achene. 
A small, clump-forming shrub. 
^ The separation of the Rocky Mountain from the western form of the Douglas fir has 
not commonly been made in this country, but there appears to be such a good basis for 
this separation, not only ecologically but taxonomically, that it is here made. Reference 
to Henry and Flood (278) and Frothingham (204) ^vill show the following characteristics 
to separate the two species: P. taxifoUa — (1) Rapid growing: (2) wide crown: (:3) 
produces a second leading shoot in summer and this late growth makes it susceptible to 
injury by late frosts: (4) foliage more regularly disposed in two ranks, soft to touch: 
(5) leaves thin, under surface fiat, no idiobfasts present; (6) leaves contain geraniol, and, 
consequently, smell like pineapple; (7) young cones green to pink, bracts erect; (8) cones 
3 to 4 inches long; (9) wood straight, light, durable, excellent timber; (10) torus of 
bordered pits centrally placed, wood readily permeated by creosote; (11) germination of 
seed poor; (12) attacked by CJiermes; (13) growth rate twice that of the other species, 
timber yield 4 to 10 times that of the other; (14) will grow in England but not New 
England. P. glauca — (1) Less rapid growing; (2) crown narrow, compact, pyramidal; 
(3) does not produce a second leading shoot, growth completed early in the season, and, 
consequently, not susceptible to frost: (4) foliage less regularly disposed in two ranks; 
(5) leaves thick, under surface convex, idioblasts present: (6) leaves contain bornyl ace- 
tate and, consequently, smell like turpentine ; (7) young cones brilliant red, bracts 
spreadins and reflexed ; (8) cones 2 to 3 inches long; (9) wood irregular in structure, 
strong and durable, rough timber; (10) torus of bordered pits pressed to one side, wood 
not readilv permeated bv creosote; (11) germination of seed much better and sooner than 
the other ' species ; (12) not attacked by Chermes ; (13) growth rate about half that of 
the other species, timber yield much le^«: than that of the other si)€cies ; (14) will not 
grow in England, but will grow in New England. 
