59 THE PLANTS OF THE GRAMPIANS. 
the scientific periodicals, which have been written by myself, ` 
in relation to this subject, attention has been principally ` 
given to the relative altitudes at which the different indige- 
nous plants commence or cease to grow. Thus, in the “ Re- | 
marks on the Geographical Distribution of British Plants," 
an imaginary division of Britain was made into five ascending 
regions, (plains, uplands, midlands, sub-alps, alps), and the 
range of each species was shown approximately in an ap- 
pended table, by naming the highest and lowest of the re- 
gions in which it had been observed. 
The advantages of this method over the plan of stating 
absolute heights in figures, are twofold. First, the relative 
heights are more easily ascertained ; for, without any trouble 
of measurement or calculation, a few lists of species made 
in ascending and descending mountains, will soon give à 
botanist tolerably accurate notions respecting the compara { 
tive altitudes attained by the more frequent species, or their d 
limits relatively to each other. "Thus, by such lists, it would 
soon appear that in ascending the Highland mountains, 
Cytisus scoparius was lost sight of before Genista Anglica, the - 
Genista before Erica Tetraliv, the Erica before Calluna vul- E 
garis, the Calluna before Vaccinium Vitis-Idea, this Vacct 
nium before Vaccinium Myrtillus, and the latter before Saliz 
herbacea; and so many ascending stages of vegetation might i 
be made, each successively characterized by the presence of | 
some, and the absence of others of these shrubs. The heights £ 
attained by other plants might also be shown relatively t° 
the heights of these shrubs, or of each other, by stating that ` | 
they cease to grow between the upper limits of the Cytisus 
and Genista, the Genista and Erica, the Erica and Callunt, 
or otherwise, as the case may be. Secondly, the relative ` 
heights of any two or more of the commoner species i 
remain pretty near the same over a considerable tract d 
country; and, consequently, on their limits being ascertained j 
in one or two places, the same may be inferred in other parts : 
of Britain, although with less of absolute certainty as the dis- | 
tance increases. For instance, if we observe that Diet 
