16 INTRODUCTION. 
floating germs of vegetation, which soon clothe the rough rock with verdure of a 
humbler kind, and ultimately, by the growth and decay of successive generations, 
form a soil for the sustenance of the higher forms of vegetable life. 
d. Another important requisite is moisture. But the arid sands of the great 
African desert are not absolutely destitute of vegetable life. Even there, certain 
species of Stapelia are said to flourish, and those dreary regions, where neither rain 
nor dew ever falls, are occasionally enlivened by spots of verdure, like islands in 
the ocean, composed of these and kindred plants. 
ce. Extremes of heat are not always fatal to vegetation. In one of the Geysers 
of Iceland, which was hot enough to boil an egg in four minutes, a species of 
Chara has been found, in a growing and fruitful state. A hot spring at the 
Island of Luzon, which raises the thermometer to 187°, has plants growing in it 
and on its borders. But the most extraordinary case of all, is one recorded by 
Sir J. Staunton. ‘At the Island of Amsterdam a spring was found, the mud of 
which, far hotter than boiling water, gave birth to a species of liverwort. Other 
similar instances are on record. 
Ff: Nor are the extremes of cold fatal to every form of vegetation. The rein- 
deer lichen, of Lapland, grows in vast quantities among almost perpetual snows. 
And far in the arctic regions, the eternal snows are often reddened, for miles in 
extent, by a minute vegetable of the Algz tribe, called red snow, of a structure 
the simplest that has yet been observed, consisting of a single round cell contain- 
ing a fluid. 
g. Light is also a highly important agent in vegetation; yet there are plants 
capable of flourishing in situations where it would seem that no ray of it ever 
entered. Mushrooms, and even plants of higher orders, have been found growing 
amidst the perpetual midnight of deep caverns and mines. Sea weeds of a bright 
green color have been drawn up from the bed of the ocean, from depths of more 
than 100 fathoms. 
13. The vegetable kingdom is no less remarkable for its rich 
and boundless variety, than for its wide diffusion. Plants differ 
from each other in respect to form, size, color, habits, structure, 
and properties, to an unlimited degree, so that it would be diffi- 
cult, indeed, to find two individuals, even of the same species, 
which should perfectly coincide in all these points. 
a. Yet this variety is never abrupt, never capricious; but here, as, in other 
departments of nature, uniform resemblances are so blended with it, as to lay an 
adequate foundation for Systematic Botany. 
14. The same causes which affect the general increase of 
plants, exercise, also, an important influence in determining their 
character. Hence, every climate has not only its own peculiar 
degree of vegetable activity, but also its peculiar species. 
a. Other causes, besides temperature, are efficient in determining the species of 
