216 NOTICES OF BOOKS. 



of omission, rather than the want of skill, that have frustrated endea- 

 vours. Many of these errors have been unavoidable, it is true ; but, 

 on the other hand, the foundations of the division must be sought in 

 a far more laborious accumulation of facts than anv one has hitherto 

 ventured upon. The fact that there are very few areas of the globe 

 at all rich in species, of the extent of ten square degrees, that have not 

 yielded upwards of 2-3000 species of plants now deposited in Eu- 

 ropean herbaria, warrants our belief that the materials do exist. The 

 only countries of that or greater extent not yet explored at all, and 

 from which collections can be brought which would alter any con- 

 clusions capable of being drawn from materials now in Europe, are 

 West Brazil. New Guinea. West China, and Central Africa ; and these 



territories 



thousand species have been collected, which renders it extremely impro- 

 bable that their vegetation presents many novel features of more than 

 generic interest. 



Chapter 26. Sketch of the vegetation of different countries in regard 

 to the probable Origin of their Species, Genera, and Families. 



The first subject investigated in this chapter is the origin of the 

 existing European plants. Under this head, the merits of Edward 

 Eorbes*s Essay on the connection of the existing Eauna and Elora of 

 the British Isles, with the Gedlogical changes which have affected 

 their area, especially during the' northern drift, etc. (Mem. Gcolog. 

 Surv. vol.i.), is fully discussed and highly appreciated. Porbes's argu- 

 ment is indeed made the basis of a complete review of this hypothesis, 

 which is illustrated by the observations of others, and of M. De Can- 

 dolle himself, who accepts nearly all its conclusions, and applies its 

 principles to other Floras. This is followed by arguments in favour 

 of the same views, derived from other sources, and especially from the 

 distribution of species, which M. de CandoUe thinks may possibly have 

 been created on the Continent since Great Britain was separated from 

 the Continent, and Ireland from Great Britain. He assumes this to 



be the case with the Composite and some allied families, because he 

 finds that the species of these sensibly diminish in Great Britain, and 

 still more in Ireland.* 



"We suspect that this diminution may be so easily accounted for by climatic 

 causes that it affords no proof of Porbes's hypothesis, even did it not require the 

 otherwise gratuitous asaumption of the relative late creation of the Order in ques- 

 tion, M. dc Caudolle indeed appreciates this objection, and endeavours to explain it 

 away, but his reasoning is not satisfactory. 



