CURRENT LITERATURE. 



Phytogeographic Survey of North America. By John W. 

 Harshberger. Leipzig and New York. 191 1. Pp. 790, plates 

 18, figures 32, map i. 



The book with the above title is Volume 13 of Die Vegetation 

 der Erde series of Engler and Drude. The contents of the 

 volume are divided into four parts. Part first : History and 

 Literature of the Botanic Work and Explorations of the North 

 American Continent. Part second : Geographic, Climatic and 

 Floristic Survey. Part third : Geologic Evolution, Theoretic 

 Considerations and Statistics of the Distribution of North Ameri- 

 can Plants. Part fourth : North American Phytogeographic 

 Regions, Formations, Associations. 



The geographical, historical and theoretical considerations, ex- 

 clusive of the very complete index, occupy approximately one-half 

 of the volume. From these one might select some interesting 

 speculations. For example, there were three great waves of 

 vegetation after the retreat of the ice sheet, being in order of 

 progress, the peat bog, the tundra and the coniferous forest. The 

 northern extension of the conifers in the West was much slower 

 in point of time than in the East, because of the longer continu- 

 ance of local glaciation. That is to say, the boreal climate per- 

 sisted so much longer in the West that the coniferous forest had 

 time thoroughly to establish itself over the whole region before 

 the present climatic conditions obtained. Once established it 

 held the ground by mere pre-emption. 



The author describes the probable advance of the members of 

 the Atlantic Forest from their post-glacial centre of distribution 

 in the Southern Alleghanies. His order of northern extension, 

 however, does not correspond with the northern limits of the 

 same species as given in Sargent's "Manual," or in the publi- 

 cations of Canadian botanists. He believes that the Bald Cypress, 

 Longleaf Pine and the Loblolly Pine came down from the hills 

 to the westward and occupied the Costal Plain. 



The treelessness of the prairies is due, according to the author, 

 to the previous pre-emption of the soil by the matted grasses, and 



