DE CANDOLLE^S GEOGRAPHIE BOTANIQUE, 69 



considers the changes which may have taken place in the hab- 

 itation of species, and discusses with great fullness the whole 

 subject of naturalization, the obstacles in the way, the causes 

 and means of transport, and the interchanges which have been 

 efeected between the New and the Old Worlds. Chapter ix. 

 is a very long and interesting one, on the geographical origin 

 of the principal cultivated plants, not only those intentionally, 

 but also those unintentionally cultivated by man, — a chapter 

 full of valuable matter, carefully collected and well discussed.^ 

 Chapter x. treats of disjoined species, — those occupying two 

 or more widely separated areas, and not in intermediate 

 stations. Chapter xi. discourses of the early condition and 

 probable origin of the existing species ; and brings out the 

 various facts which go far to prove the geological antiquity of 

 the greater part of existing species ; and that their creation 

 was probably successive. Chapter xii. treats of genera and 

 their geographical distribution, and maintains the view (in 

 which we by no means coincide) that genera are truly natu- 

 rally-limited groups, even more so than species. Chapter 

 xiii. is devoted to the distribution of the species of a genus 

 within its area. Chapter xiv. treats of the extent of surface 

 occupied by genera. Chapter xv. discourses of the origin and 

 duration of genera. Chapters xvi.-xix. treat of families, as 

 to their area, geographical limits, the distribution of species 

 within the area of the family, etc. 



The Third Book is devoted to Geographical Botany, or the 

 characters of different countries considered as to their veg-eta- 

 tion. Chapter xx., of the characters of the vegetation of a 

 country ; considered, in Chapter xxi., as to the relative num- 

 bers in the great classes respectively. Chapter xxii., compari- 

 son of different countries in respect to those natural orders 



1 It is singular that M. De Candolle should be so slow to abandon the 

 idea that the aborigines of Carolina, or any other part of North America, 

 cultivated or knew anything of the Potato, which, if Raleigh obtained 

 them in Carolina, were certainly imported thither. But, though our 

 aborigines had no Potatoes, they had Pumpkins or Squashes and Beans, 

 which all writers upon the history of cultivated plants have overlooked 

 except the late Dr. Harris. 



