N ORA.Y \M' HOOKER OK mm ROCKY MOUNTAIN FLORA. 9 



arotio flora. Anj list will therefore be to some extent arbitrary. For 

 iple, in the Atlantic alpine li>t. while Cardamine beUidjfolia, Silene 

 Slbbaldia procumbent, CfnaphaHum supinum. Rhododendron Lappo- 

 LapponioOj and the like, are strictly and exclusively 

 alpiue, Arenaria Ghreenlandica and Genm radiatum [PeehU) are included 

 for reasons which any botanist who baa ascended these mountains will 

 appreciate, although a form of the Arenaria sparingly occurs at low 

 levels in Southern New England and New York, and both on the bops 

 of the higher Alleghanies, where no characteristically alpine Bpecies 

 accompany them, and where Buch summits as arc bare of trees are not 

 woodless on account of cold <>r any other incident of mere elevation. 

 Notwithstanding the geographical extent of the country over which it 

 read, the North American alpine flora Is meagre in Bpecies com 

 • i with that of Europe. This will abundantly appear in the com- 

 parison t<> be made in another part of this report. Reasons connected 

 with geographical configuration and climate will account for this, but it 

 must also be remembered that the botany of the European Alps is 

 >ughly known: that of the Rocky and other western mountains 

 e imperfectly so. 



II.— Tin: FoKi.si REGION. 



1. Its U 



The most conspicuous portion of the vegetation of a country, and the 



important under more than one point <>f view, is its trees. Their 



importance is most manifest in the district under consideration, where 



than a quarter of the area is capable of producing them, and of 



whir . to tires and other causes, only about hair of what Major 



ties as •• tin i i>er regions B are actually covered with forest 



krd the north the case is men 3 altered, especially in British 



America, where, in a wide tract with moderately abundant and well 



distributed rainfall, and summers not excessively warm, the Atlantic 



and Pacific forests join and intermingle. Southward, and indeed nearly 



up to th<- northern boundary of the United states, trees are borne only 



on the mountains and high plateaux, and along the immediate banks of 



from the* 



The species of the whole Rocky Mountain region 1 taken in the wi< 



inch may claim the name of trees — even of tree-like shrubs — 

 an- not long t<> enumerate. 1 They are th< 



. Willd. IfortM microphyUa^ Buckley. 



\ndidentatum, Nutt. Populue angustifolia, James, 



ch. Populiu bah . L. 



- 3 



