799 



level in any part of Britain, the lowest altitude is indicated by yards, 

 and usually reckoned by steps of 50 yards. 



" The eighth line shows the highest limit ascertained for the spe- 

 cies, also by steps of 50 yards, without affecting more minute exact- 

 ness. There are many plants of the plains or low grounds, not 

 ascending the mountains, the upper limits of which can only be 

 guessed in general terms. Thus, for example, the true upper limits 

 of the Clematis, Euonymus, Tamus, &c., not having been exactly as- 

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

 yards. 



" The ninth line is intended to show the range of mean annual 

 temperature under which the species grows in Britain. 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 annual temperature of the air (that of the ground being nearly 

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

 Fahrenheit'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 

 degree is deducted from inland localities under the same latitude, and 

 one degree also for each hundred yards of elevation above the level of 

 the sea. In applying this rule to particular species, however, some 

 slight allowance has been made for situation. It is probable that the 

 temperature of the atmosphere, with us, decreases more rapidly than 

 one degree for one hundred yards of elevation, while that of the earth 

 decreases less rapidly. On the Highland mountains, between 3000 

 and 4000 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 unimpeded by vegetation. 



" The tenth line, continued into a paragraph, is intended to show 

 the civil claims and local situation of the species, in accordance with 

 a scale of terms ; also to give any other brief notices which may seem 

 desirable or necessary. The first word is one taken from the follow- 

 ing series of terms, used to express the civil claims of the species : — 



" 1. Native. — Apparently an aboriginal British species ; there being 

 little or no reason for supposing it to have been 

 introduced by human agency. Examples : Cory- 

 lus, Calluna, Bellis, Teesdalia. 



" 2. Denizen. — At present maintaining its habitats, as if a native, 

 without the aid of man, yet liable to some sus- 



