GEOGRAPHY OF PLANTS. 



plants. Yet it must be distinguished from this ; and when 

 a sure foundation of facts is laid and arranged, it exerts an 

 essential influence on the science of the cultivation of gardens 

 and fields, on the rearing of forests and other civil occupa- 

 tions. 



391. 



We may investigate the laws of the distribution of the fa- 

 milies and tribes of plants in different climates by two me- 

 thods. 



In the first place, we divide the surface of the Earth into 

 certain zones, in which we seek for the plants that are pro- 

 duced, and thence draw general results. This method is in- 

 deed a laborious one, and is especially difficult on this ac- 

 count, that we are not yet completely acquainted with all the 

 parts of every zone of the earth ; while the lower families of 

 plants have commonly been neglected by most travellers. 

 Yet we can draw conclusions, with some probability, respect- 

 ing unknown plants from those that are known ; at least, this 

 method leads to greater certainty than the following, on which 

 only, however, most of our labours have been conducted. In 

 this second method, we place the Floras of countries of diffb- 

 rent climates before us ; we compare the plants which they 

 contain, and in this way form conclusions respecting their dis- 

 tribution. But, as we are not in possession of complete Flo- 

 ras of all countries and their individual regions, it cannot but 

 happen that false inferences and contradictions will arise, 

 while we do not take into account the productions of neigh- 

 bouring countries, or of those that lie between the districts 

 which have been examined. Besides, we can only make use 

 of the Floras of particular degrees of latitude and longitude, 

 but not those of the whole zone ; because most of the com- 

 pilers of Floras have been acquainted \yith the products of 

 vegetation only within a certain circle. 



392. 



Without entering, in this place, pto the history of plants, 

 we may state it as the fundamental law of the geography of 



