REVIEWS 751 



The authors recognize seven species and one variety ; three species 

 and one variety being American and four species Asiatic. American 

 dendrologists have almost without exception recognized but two Amer- 

 ican species, namely, the widely distributed Pseiidotsuga Douglasii, 

 Carriere^ and Pseudotsuga macrocarpa, Mayr, of very limited dis- 

 tribution. 



In this revision the authors recognize Pseudotsuga glaiica, Mayr, 

 as a valid species and Pseudotsuga Douglasii, var. ccesia, Schwerin, as 

 a valid variety. The Pacific coast tree, the green Douglas, is considered 

 quite distinct from the Colorado tree, the blue Douglas, and the tree 

 of the Northern Rocky Mountain region, recognized as a valid variety, 

 is considered intermediate between the green and the blue Douglas. 

 The green and blue trees are so distinct the authors believe the eleva- 

 tion of the blue variety to specific rank is clearly warranted. They 

 state, "The cones of the two species have a very different appearance, 

 those of the Colorado Douglas being smaller, with fewer scales and 

 bracts that bend backward about the middle. The leaves of the Colo- 

 rado form are much thicker. When the shoots are rubbed the Pacific 

 coast Douglas emits a pleasant smell of pineapple, while the odor of 

 P. glauca is strong and like turpentine. This is considered a more 

 reliable means of field identification than differences in color as the blue 

 color of the Colorado Douglas cannot be relied upon. Among other 

 minor points of difference the more ascending branching of P. glauca 

 is mentioned. 



From the forester's point of view, the distinctions in the two species 

 lies primarily in their rate of growth both in height and diameter and 

 in their difference in climatic requirements particularly in frost re- 

 sistance. The authors state that the Pacific coast tree puts on an 

 annual height increment of two feet a year and that there are few other 

 species which have this faculty for fast growth extending over a long 

 period of years. Although in England it grows best on fresh, loamy, 

 well-drained soils, it thrives much better on poor soils than generally 

 supposed, and is now considered the best exotic conifer for general 

 purposes of artificial regeneration available for use in Great Britain. 



^Pseudotsuga Douglasii, Carriere, the first name of the species under the cor- 

 rect genus is the name generally used by foresters and botanists abroad. Pseu- 

 dotsuga ta.xifoUa, Britton, founded on the earliest specific name is generally 

 used in this country and is in accord with the Vienna Rules of Nomenclature. 

 Pseudotsuga mucronata, Sud worth, has been accepted by some American 

 dendrologists as the correct binomial for this species. 



