496 X. GENERAL REMARKS. 



observed to be in Aberdeenshire, on the eastern side of 

 the island. But in the list here referred to the degrees 

 of temperature are indicated in accordance with absolute 

 height ; and consequently the names of the species are 

 placed in sequence without allowance for diflferences of 

 site and situation, either by abatement or by increase. 

 This can hardly fail to introduce some inaccm'acies into 

 the series, although they may not be very great. For 

 instance, if the highest limit of one species in Aberdeen- 

 shire becomes contrasted against the highest limit of 

 another species on or near Ben Nevis, — or the upper 

 limit of one species on a southern declivity, in Perthshire, 

 is contrasted against the upper limit of another species 

 on a northern declivity, in Easterness. 



Those sources of misposition are avoided by the assign- 

 ments of plants to the zones being made according to their 

 own relative limits, not according to absolute altitudes. 

 But in turn this method may also occasionally mislead in 

 a different manner ; because the highest observed locality 

 for a species, on any certain hiU, may or may not be the 

 highest at which it does or could grow on that hill. 

 Nothing but the discrimmation of experience, gradually 

 acquired from oft-repeated observation, can correctly 

 make the necessary allowances for these and various 

 other uncertainties and chances of error. 



It may thus be considered that some discrepancies are 

 certain to occur between any two series of names, in 

 which the plants are arranged on different rules, whether 

 according to absolute altitude, — or according to supposed 

 temj)erature, by the scale in which latitude and elevation 

 are both taken into account, — or according to their own 

 relative limits, irrespective of absolute height, &c. The 

 fact to be impressed by these remarks, is, that such dis- 

 crepancies and uncertainties will unavoidably interfere 



