436. X. GENERAL REMARKS. 



Britain. But it is inferred from the imperfect data 

 attainable, that species are not alwaj's, and perhaps are 

 not usually, most abundant at the centre of their areas. 

 Understanding the geographic area of a plant to signify 

 the whole s^jace of terrestrial surface, over -which it is 

 diffused more or less continuously, that area will include 

 certain ranges of latitude and longitude, — of climate, 

 under its manifold proportions of temperature and hu- 

 midity, — of altitude, both absolute and relative, — of mari- 

 time proximity and remoteness, &c. Such ranges may 

 be mentally conceived and represented as linear or cate- 

 narian. On the contrary, the area of a plant must have 

 width as well as length, and should be mentally conceived 

 as more or less approximating to a square form, occasion- 

 ally rounded, occasionally elongated. 



It is suggested for further examination, that many of 

 the British species are most abundant on the western 

 side, rather than towards the centre, of their present 

 (curtailed ?) geographic areas. But looking on the 

 western side of their areas, and considering it as a line 

 traced from south to north, or reverseij^ the species may 

 perhaps usually be found most abundant and best deve- 

 loped near the middle of that line. To this no doubt 

 many seeming exceptions might be pointed out ; because 

 the linear range of altitude will cross and interfere with 

 that of latitude ; and some other conditions also come in 

 to modify the single one of latitude. 



Whatever may be the place of greatest abundance of a 

 species, and closest repetition of special localities for it, 

 the localities usually become more and more disjoined, 

 and often less productive also, in proportion to distance 

 from that j)lace. Gradually it becomes a "rare plant," 

 appearing only in few spots, with wide interspaces ; and 

 those few spots probably producing few individual exam- 



