16 INTRODUCTION. 



floating germs of vegetation, -niiich 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 tlie sustenance of the higher fonns 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 drcaiy regions, where neither rain 

 nor dew ever falls, ai-e occasionally enlivened by spots of verdui'e, like islands in 

 the ocean. 



c. Extremes of heat ai-e not always fatal to vegetation. In one of the Geyscii's 

 of Iceland, which was hot enough to boil an egg in four minutes, a species of 

 Chara has been found, in a gro'^ving and fniitful 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 

 sunilar instances are on record. 



/ Nor are the exti-emes of cold fatal to eveiy fonn of vegetation. The rein- 

 deer lichen, of Lapland, grows in vast quantities beneath 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 Algte tribe, called red snow, of a sh-ucture 

 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 flourisliing in situations where it would seem that no ray of it ever 

 entei'cd. 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 vogotablc kingxlom is no less remarkable for its rich 

 and boimcUess variety, than for its wide difTusion. Plants diiler 

 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. 



fl. 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 

 adeq^iate foundation for Systematic Botany. 



14. The same causes which affect the general increase of 

 )ilants, exercise, also, an important influence in determining their 

 diaracter. Hence, every climate has not only its own 2^^culiar 

 degree of vegetable actiA-ity, but also i{s pecidiar species. 



a. Other causes, besides temperature, are efficient in determinuig the species of 



