V. INEQUALITIES OF DISTRIBUTION. 437 



pies of the species. In this manner plants gradually- 

 attenuate their distribution into isolated spots on the 

 outskirts of their areas, like so many advanced points or 

 positions, beyond which the same species is no more 

 seen. Occasionally, these outlying localities are so far 

 distant as to seem quite disconnected. This is more par- 

 ticularly the case with alpine plants, where the mountains 

 on which they grow are disjoined by wide interspaces of 

 low countr}^ having a climate unsuited to alpine plants, 

 and a larger vegetation among which such plants would 

 vainly struggle to hold their ground. 



It is that tendency of species to attenuate into small 

 detached localities, as they approximate towards their 

 vanishing points, which is difficult to represent correctly 

 to the eye on paper. Dots would do this more correctly 

 than lines. But maps ordinarily bear so very small a 

 propoi'tion to the actual geographical surface, that visible 

 dots on them must often unavoidably exaggerate the 

 localities, and minimize the interspaces, into very dispro- 

 portionate reijresentations of the truth. And when lines 

 are traced upon maps, so as to connect the outl}ang 

 localities, they falsely seem to represent an abrujitness of 

 limit, and to enclose a continuity of area, neither of 

 which has any real existence. On the other hand, if the 

 most separated and outlying localities are not taken in, 

 the line is then drawn too short of the actual range and 

 limits of the species. Lines must thus enclose either too 

 much or too little. 



The same tendency towards detached points of cessa- 

 tion, by isolated and small localities, often renders it 

 matter of much uncertainty at what particular latitude, 

 or at what particular elevation, species should be stated 

 to cease or to commence. In many cases it is not an 

 easy matter to make sure that the most boreal or most 



