V. INEQUALITIES OF DISTRIBUTION, 435 



the tendency of species to become less plentiful towards 

 tlieir areal limits, as noticed below. 



3. Geograpliical limits of Species. — As no flowering 

 plants are- distributed over tbe whole earth, the areas of 

 all may be said to have terminal limits, geographical, 

 climatal, &c. Phyto-geographers have endeavoured to 

 trace out a correspondence and connexion between the 

 ai'eas of species and the lines of latitude and longi- 

 tude marked on maps ; and also to connect the boun- 

 daries of those areas with lines which are believed 

 to represent similarities of cUmate, or other conditions of 

 physical geography. An incorrect idea is in this manner 

 fostered and promulgated, that the limits of plants are 

 abruptly bounded, and that they can be properly rei)re- 

 sented by lines traced upon maps. This is so imperfectly 

 true, as to be almost false. Who has ever found such 

 lines in England ? Who has ever discovered or traced 

 out any such lines on the actual land, or in the actual 

 vegetation, in any part of the world ? Notwithstanding 

 the statements and representations of those who make 

 books and maps at home, the botanists who. look out 

 upon the realities of nature, seldom or never find the 

 limits of species running in lines. 



The usual manner of distribution and cessation is 

 quite difierent. The whole area of a plant being under 

 view, its special localities are usually found to be most 

 approximated and most productive about the middle of 

 its range, either of latitude or of elevation. The middle 

 of the range may be near tlie centre of the area, or not 

 so ; and the two expressions are therefore not to be held 

 synonymous. No verj' confident assertion can j'et be 

 made on this point, from want of sufliciently clear and 

 precise data respecting the census of plants beyond 



