202 
INFLUENCE OF CLIMATE ON VEGETATION. 
house," as applied to the plants of tropical and temperate climates, be given up, and exotic 
plants classified anew, into a greater number of groups; so that universally, and not partially, 
the variety of climate required may be understood, and the knowledge practically applied. 
These views on the subject of climate are in unison with the scheme of a somewhat 
recent work on the geography of plants.* In this volume the climatic groups of plants are 
more numerous than those we popularly allow ; and, consequently, the range of temperature, 
correspondent with each group, is much more limited than we have been under the necessity 
of associating with the terms "stove " and " greenhouse," as applied to exotic vegetation. 
I cannot, therefore, but think that it would be extremely useful to those cultivators, who 
may not have access to Meyen's work above alluded to, if some little space be devoted to 
the explanation of his scheme, and some of the particulars of the climates corresponding to 
his zones and regions : not that these supply exactly what the cultivator seems to require 
in recasting his groups of exotic plants, but because the scheme itself is calculated to lead 
the mind in the right direction, substituting, as it does, an eightfold for a threefold division 
of the earth. 
Meyen divides the surface of the earth from the equator to the poles into eight zones, 
characterised by a certain mean temperature, and these zones are again divided into regions 
from the level of the plains to the snow line. It is well known that in proceeding from the 
equator towards the poles the temperature diminishes in something like ratio ; and that in 
ascending from the sea level towards the point of congelation, the same result is found. 
Hence, if there be sufficient altitude, though it be in the tropics, there will be perpetual 
congelation, equally as in the arctic regions ; and further, there will be a relation between 
the intermediate points of latitude and altitude. 
It was because the common astronomical division of the surface of the globe into the 
three zones — the torrid, temperate, and arctic — was not found sufficient for the purposes 
of botanical geography, the zones being too few and extensive, that Meyen proposed to 
divide each hemisphere into eight smaller zones founded upon the common division, and 
to divide the altitudinal range of vegetation into a corresponding number of regions. 
And it is a fact worthy of the consideration of cultivators, that not only is it found that 
the zones are characterised by a peculiar vegetation ; but there is a parallelism betw^een the 
horizontal range and the vertical range of vegetation, " in exact correspondence with 
the parallelism between the decrement of heat from the equator to the poles, and from 
the plains to the peaks of the mountains." 
It must, however, be borne in mind that divisions such as those referred to, are but 
approximations ; they are of necessity arbitrary ; and the zones and regions themselves, 
blend insensibly with each other. It is admitted that there is often on different 
mountains in the same latitude, a difference of several hundred feet in the height of the 
same vegetation ; so that in fact, there is no such exact and regular distribution of vege- 
tation as Meyen assumes. Nevertheless, these assumed divisions afford certain data to 
the cultivator, which are to him of the utmost value, as showing the nature of the 
relation existing between the vegetation of one part of the globe, and that of another. 
It appears that beginning at the polar zone, the snow-line rises about 1900 feet for 
each of the before-mentioned eight zones. Thus we should have the snow-line at an 
elevation of 15,000 or 16,000 feet in the equatorial zone, which is found to be near the 
truth, the snow-line of Cotopaxi being at an elevation of 15,646 feet, and on Chimborazo, 
at 16,000 feet. This increase of 1900 feet for each zone in the limits of vegetation, 
corresponds to the regions into which the mountain vegetation is divided. This, the 
following table will more clearly exhibit. 
* Outline of the Geography of Plants, by F. J. F. Meyen, Ph. D., M.D., translated for the Ray Society. 
