INTRODUCTION. 3 



but the observations of botanical travellers are continually 

 filling up the outline which was first sketched out some fifty 

 years ago by Baron Alexander von Humboldt, who is con- 

 sidered as the founder of the science. 



De Candolle and Schouw have mapped out the whole sur- 

 face of the globe into botanical kingdoms ; and Meyen has 

 divided it into eight botanical zones. The boundaries of 

 the different and ever-varying forms of vegetation may thus 

 be marked out more definitely than could possibly be done 

 in the wider divisions of the five astronomical zones ; and a 

 closer connection can thus be traced between the gradual 

 changes in the appearance of vegetation, and the equally 

 changeable varieties of temperature. 



Still the character of vegetation is affected by so many, 

 and often counteracting influences, besides that of the tem- 

 perature, such as the absence or presence of moisture, pre- 

 vailing winds, and a suitable or unsuitable soil, that, after 

 all, an approximation to the truth is all that can be attained. 

 Some kind of framework is necessary for methodizing know- 

 ledge, but Nature will not be tied down by too strict rules ; 

 so that the flowers which are named as chiefly characteristic 

 of one zone, are often found wandering into the next, and it 

 is as impossible to assign a definite limit to them, as to mark 



