48 REVIEWS. 



families of plants in a geographic point of view ; and by the latter, the con- 

 sideration of different regions of the earth with respect to the vegetation 

 which clothes them. The first division, or Geographic Botany, offers the 

 widest field of research, and forms, indeed, the bulk of the treatise, occupy- 

 ing sixteen of the chapters, and filling nearly 1100 pages. We can 

 only briefly allude to a few of the subjects treated of. The first chapter, a 

 very important one, runs over 300 pages, and discusses, under the varied 

 circumstances which influence the dispersion of plants, their limitation on 

 the plains and on the mountains. The limits occupied by spontaneous 

 plants on the plain, or at a moderate level above the sea, in a direction 

 towards the pole, and towards the equator, are illustrated by detailed 

 accounts of certain well-known annual, perennial, and ligneous species. 

 Each of the indicated limits is then separately discussed, and this is fol- 

 lowed by general considerations on the polar and equatorial limitation of 

 each description of vegetable. We have then the limits in altitude of spon- 

 taneous plants similarly treated ; and, finally, cultivated plants, whether on 

 mountain or plain, are subjected to a like analytical examination. 



The next chapter discusses what the author calls the "form" of the 

 habitat of species — namely, the differences in the diameters of the area occu- 

 pied by different species, when the line is drawn east and west, or north 

 and south, or in some intermediate directions. Some curious facts are noted 

 on this subject, and obviously this chapter deserves to be more extensively 

 worked out. The author has limited his observations to the species con- 

 tained in the eighth, ninth, and tenth volumes of the " Prodromus," as w 

 offering sufficient illustration of his subject, and finds that of the 8,495 

 species contained in those three volumes, there are only 116 which present 

 any very marked differences (four times at least) between the lengths of the 

 opposite diameters of their areas. The remaining 8,372 species appear to 

 occupy more or less circular areas — a remarkable fact. It must be observed, 

 however, that this examination refers exclusively to certain orders of the 

 Corollijlorce, whose distribution can hardly be taken as fairly representa- 

 tive of that of Phanerogamous plants in general. Of the 116 species se- 

 lected by M. de Candolle, sixty-eight extend east and west, and forty- 

 eight in a naiTOW line north and south. One should hardly have a priori 

 anticipated so nearly equal a division of the number, it seems so much 

 more natural that a species should extend along the parallels of latitude, or, 

 at least, in the isothermal lines, than along those of longitude. We are thus 

 taught that other causes than those of annual temperature powerfully influ- 

 ence the natural dispersion of plants. The most potent, probably, are 



