44 BULLETIlSr 680, U. S. DEPARTMENT OF AGEICULTURE. 



Seedlings occur, however, only occasionally, and most frequently in 

 deep shade on wet moss and decaying wood. The generally scattered 

 occurrence of this species and the fact also that only female trees bear 

 fruit, which is much eaten by birds, doubtless account for the sparse, 

 often rare, occurrence of seedling growth. 



LONGEVITY. 



The extreme age attained by the western yew has not been deter- 

 mined. Its growth in height and diameter is very slow, particularly 

 under deep shade; but even here the tree maintains itself most per- 

 sistently, indicating that it is long-hved. Comparatively few. sound 

 trees of even moderately large size appear to have been studied. 

 Trees 6 inches in diameter are from 75 to 90 years old, whUe trees 

 from 12 to 20 inches in diameter are from 140 to 245 years old. The 

 largest specimens are believed to be at least 350 to 375 years old. 

 Owing to the fact that the largest trees are so often punky at the 

 center it will be difficult to determine satisfactorily the extreme age 

 of this yew. 



KEY TO GENERA AND SPECIES. 



Leaves needle-shaped and borne singly: 



Bark of the trunk very thin, smooth or loosely scaly and purple. . Taxus hrcvifoUa 

 Bark of the trunk rough; thick and furrowed, or thinnish and with firm scales — 

 Leaves with distinctly formed delicate stems — 



Cones I to 1^ inches long; fiat leaves in 2 thin lines Tsuga heterophylla 



Cones 1^ to 3 inches long; rounded leaves not in lines Tsuga mertensiana 



Leaves contracted at the base but without distinctly formed stems — 



Cones bearing conspicuous, 3-pointed bracts Pseudotsuga taxifolia 



Leaves in brushlike clusters of from 12 to 40 — 

 Cones about one-half an inch long and without exserted bracts. .Larix laricina 

 Cones 1 to 2 inches long and with exserted bracts — 

 Trunk bark thick, from 3 to 6 inches thick and deeply furrowed, 



Larix ocddentalis 

 Trunk bark thin, from one-half to three-fourths of an inch thick and slightly 



furrowed Larix lyallii 



Leaves scalelike, borne in pairs and closely overlapping each other: 



Cones borne near the ends of twigs; seeds winged on two sides Thuja plicata 



Cones borne at the ends of twigs; seeds winged at one end Lihocedrus decurrens 



