62 EXPLANATIONS OF THE FORMULA. 



plains or low grounds, not ascending the mountains, the 

 upper limits of which can only be guessed in general tenns. 

 Thus, for example, the true upper Umits of the Clematis, 

 Euonymus, Tamus,&c.,not having been exactly ascertained, 

 they will be indicated in general terms, at 100 or 200 

 yards. 



The ninth line is intended to show the range of mean 

 annual temperatm'e xmder which the species grows in Bri- 

 tain. It will easily be understood that this cannot be more 

 than an approximation to the true climate. The estimate 

 is made in the following manner. The mean amiual tem- 

 peratiu-e of the air (that of the gi'ound being neai"ly the 

 same), on the south-west coast of England, is taken at 52° 

 of Fahi'enheit's scale ; that of the south-east coast, at 51° ; 

 the estuaries of the Thames and Severn, at 50* ; those of 

 the Humber and Mersey, at 49° ; those of the Forth and 

 Clyde, at 48° ; the extremities of the Caledonian Canal, at 

 47° ; the north coast of Scotland, at 46°. One degi'ee is 

 deducted from inland localities under the same latitude, 

 and one degi'ee also for each hundred yards of elevation 

 above the level of the sea. In applying this rule to par- 

 ticular species, however, some slight allowance has been 

 made for situation. It is probable that the temperatm'e of 

 the atmosphere, with us, decreases more rapidly than one 

 degree for one hundred yards of elevation, wliile that of the 

 earth decreases less rapidly. On the Highland momitains, 

 between 3,000 and 4,000 feet, the temperature of springs 

 varies but little with altitude, during the summer months ; 

 being usually 37° or 38°, where the exit of the water is mi- 

 impeded by vegetation. 



The tenth line, continued into a paragraph, is intended 

 to show the civil clauns and local situation of the species, 

 in accordance with a scale of terms ; also to give any other 

 brief notices which may seem desnable or necessary. The 



