376 X. GENERAL REMARKS. 



or causal conditions by which plants and places are 

 connected together. In attempting to trace out such 

 relations it would be needful to oscillate between the two 

 divisions of the study, as laid down by A. De Candolle 

 and his Reviewer ; now looking to one, now to the other 

 of them, without any such decided severance being kept 

 up. Even in preliminary arrangements of the data, such 

 as constitute the staple of this treatise, relating to the 

 plants of one country, and which await similar arrange- 

 ments in other countries before they can be rendered 

 properly causal, the two abstract divisions of the subject 

 have run much together. To which of those two divi- 

 sions, it may be asked, does the ' Distributive Census ' on 

 pages 263 to 264 belong ? To either or to both, is the 

 unavoidable answer to the query. On these and other 

 considerations, the distinctions traced between geogra- 

 phical botany and botanical geography are not made 

 primary and fundamental in this work ; although it is 

 admitted that they are clear and logical in the abstract 

 idea, and can be made so in definition. 



2. On Floral Areas. 



In instituting comparisons between the floras of dif- 

 ferent countries, or between different portions of the 

 same country, too little regard has usually been given to 

 the effect of inequality of areas on the numerical values 

 and proportions of their floras. Some few pages may 

 here be usefully devoted to illustrating the influence of 

 such inequality by examples. The known flora of the 

 earth at large has been taken to include nearly 83,000 

 species (cellular plants always excej)ted) in accordance 

 with the, figures given by Dr. Lindley. The area of 

 Britain has been stated at 88,000 square miles, after 



