102 PHYSIOGNOMY OF PLANTS. 



their predominance in advancing from the equator towards 

 the poles follow a similar law of decrease in ascending moun- 

 tains situated in the equatorial regions ? Do the proportions 

 of particular families to the whole mass of Phanerogam 

 differ in the temperate zones, and on equal isothermal lines, 

 north and south of the equator ? These questions belong 

 properly to the Geography of Plants, and connect themselves 

 with the most important problems of meteorology and 

 terrestrial physics.J The character of a landscape or country 

 is also in a high degree dependent on the predominance of 

 particular families of plants, which render it either desolate 

 or adorned, smiling or majestic. Grasses forming extensive 

 savannahs, Palms and other trees affording food, or social 

 Coniferse forming forests, have powerfully influenced nations 

 in respect to their material condition, to their manners, 

 to their mental dispositions, and to the more or less rapid 

 development of their prosperity. 



In studying the geographical distribution of forms, we 

 may consider species, genera, and natural families, separately. 

 In social plants, a single species often covers extensive tracts 

 of country; as in northern regions forests of Pines or 

 Firs and extensive heaths (ericeta), in Spain cistus-covered 

 grounds, and in tropical America assemblages of the same 

 species of Cactus, Croton, Brathys, or Bambusa Guadua. 

 It is interesting to examine these relations more closely, 

 and to view in one case the great multiplicity of indivi- 

 duals, and in another the variety of organic develop 

 ment. We may inquire what species produces the greatest 

 number of individuals in a particular zone, or we may ask 



