16 INTRODUCTION. 



floating genns 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, hke islands in 

 the ocean, composed of these and kindred plants. 



e. 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 formd, 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. 



/. 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 Algce 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 mdividuals, 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, unifonn 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 determming their 

 character. Hence, every chmate has not only its own peculiar 

 degree of vegetable activity, but also its peculiar species. 



a. Other causes, besides temperature, are efiicient in determining the species of 



