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THE AMERICAN NATURALIST [Vol. XLVI 



the course of this section he expounds his own views as to the 

 origin of the North American flora, and the factors which have 

 brought about its present distribution. While this section con- 

 tains much important and interesting material, it can not be 

 said that its arrangement is all that could be desired. After a 

 perusal of the 174 pages contained in it, there is left in one's 

 mind a very confused impression of a conglomeration of geology, 

 phytogeography, and the origin of floras, together with other 

 more or less disconnected topics. A large part of this section 

 deals again with the phytogeographical areas already discussed 

 at length in the previous section, and repeated in the fourth 

 part of the book, but deals with them from the standpoint of 

 centers of distribution rather than merely from latitude. It is 

 to be regretted that the subject of the phytogeographical areas 

 has not been treated as a connected whole, and also materially 

 reduced, so as to bring out the salient points, instead of present- 

 ing a mass of details of very varying importance. 



While, as might be expected, the plants treated are for the 

 most part the flowering plants, still the lower plants are not en- 

 tirely neglected, the Alga? especially coming in for a fuller 

 treatment than is usually accorded them in works on plant dis- 

 tribution. 



As the flowering plants, especially Angiosperms, are the pre- 

 dominant plants of the existing land floras, the geological history 

 of the country before the Cretaceous is of relatively small impor- 

 tance as bearing upon the distribution of the existing vegetation, 

 since it is not until the Cretaceous, or at the earliest the Sub-Cre- 

 taceous is reached, that recognizable remains of Angiosperms 

 are met with. Professor Harshberger gives an excellent ac- 

 count, with maps, of the distribution of land and water areas 

 during the Cretaceous and their significance as affecting the 

 future distribution of North American plants. 



During the lower Cretaceous a solid land mass occupied ap- 

 proximately the present area of North America, but was sepa- 

 rated from South America by a wide gap through what is now 

 Central America, allowing free communication between the At- 

 lantic and the Pacific. At that time also there was still a broad 

 land connection with Western Europe. Throughout the north- 

 ern area both of the old and new world, it is evident that a 

 very uniform vegetation flourished, with Conifers as the predom- 



