4 
The vegetable SYSEM. 
The thlnnefl Air Is on the tops of mountains ; and its effedls on 
Vegetation are uniform and conftant there. We have feen the 
Plants of different places under equal latitudes vary greatly in ftature 
and in fpecies, though the Heat be the fame : perhaps, nay probably, 
the difference of Air makes the change ; for where that is alike. 
Vegetation is alike alfo. The high mountains of all parts of the 
world afford the fame afpedl in their Vegetables : all are low but 
hardy : we fee the Shrubs of the fame humble height on Mount 
Olympus and the Hills of Greenland; the Alps and Pyrene- 
ans, the Mountains of the Brasils and of Lapland yield the 
fime crops of vegetable nature ; nay, there Is no difference between 
the produdtions of our own Welsh Mountains, and of Ararat. 
Not only Plants of the fame heights but the fame Plants, the fame 
Species, arc found on all thefe mountains, though they are fo re- 
mote, and under fuch different latitudes. Heat cannot do this, for 
there are no Plants common to all hot countries ; and Cold is but a 
negative quality ; the want of Heat, and nothing more. The Soil 
is different on thefe various mountains ; fo it is not that which oc- 
cafions this amazing regularity and famenefs in their produdtions. 
It is therefore in the Air we are to feek the caufe : and we may 
learn from this fingle inflance its great qualities in regard to Vege- 
tation. Air is of abfolute neceffity to vegetable life, and makes a 
part of the bodies of all Plants ; as is conftantly found In their ana- 
lyfis : but it is not pure Air that ralfes them to heighth, or gives 
their fpacious Flowers : Air loaded with moift vapours, and actu- 
ated by confiderable Heat, feeds the vegetable faculties moft freely. 
CHAP. III. 
Of the Effects of Earth in Vegetation. 
E A R T H is the food of Plants ; and conflitutes their fubftance : 
from this they arife, and to this they return. Water will 
fupport fome kinds, but ’tis by means of the Earth which it con- 
tains : and Earth owes to water the power of entering the veffels in 
all 
