ILLUSTRATIONS (13). GEOGRAPHY OF PLANTS. 279 



The numerical relations of the forms of plants, and the laws 

 observed in their geographical distribution, admit of being 

 considered from two very different points of view. When we 

 study plants in their arrangement according to natural fami- 

 lies, without regard to their geographical distribution, the 

 question arises: What are the fundamental forms or types 

 of organization, in accordance with which the greater number 

 of their species are formed ? Are there more Glumaceae than 

 Composite on the earth's surface? Do these two orders of 

 plants combined, constitute one-fourth of the phanerogamia ? 

 What numerical relation do monocotyledons bear to dicoty- 

 ledons? These are questions of general phytology, a science 

 that investigates the organization of plants and their mutual 

 connection, and therefore has reference to the now existing 

 state of vegetation. 



If, on the other hand, the species of plants that have been 

 connected together according to their structural analogy, are 

 considered not abstractedly, but in accordance with their 

 climatic relations, and their distribution over the earth's sur- 

 face, these questions acquire a totally different interest. We 

 then examine what families of plants predominate in the torrid 

 zone more than towards the polar circle over other phanero- 

 gamia? We inquire, whether the Composite are more nume- 

 rous in the new than in the old world, under equal geogra- 

 phical latitudes or between equal isothermal lines ? Whether 

 the forms which gradually lose their predominance in advanc- 

 ing from the equator to the poles, follow a similar law of 

 decrease in ascending mountains situated in the equatorial 

 region? Whether the relations of the different families to 

 the whole mass of the phanerogamia differ under equal iso- 

 thermal lines in the temperate zones on either side of the 

 equator? These questions belong to the geography of plants 

 properly so called, and are connected with the most important 

 problems that can be presented by meteorology and terrestrial 

 physics. Thus the predominance of certain families of plants 

 determines the character of a landscape, and whether the 

 aspect of the country is desolate or luxuriant, or smil- 

 ing and majestic. Grasses, forming extended Savannahs, 

 or the abundance of fruit-yielding palms, or social coniferous 

 trees, have respectively exerted a powerful influence on the 

 material condition, manners, and character of nations, and OB 

 the more or less rapid development of their prosperity. 



