452 PLANT DISTRIBUTION 



the flora of that region. The animals native to a region 

 considered all together constitute its fauna. A particular 

 species of plant or animal may occur in the flora or fauna 

 respectively of many regions and be associated with a 

 different set of other species in each. This illustrates 

 the universal fact that the range of any particular species 

 is distinctive of it but rarely corresponds accurately with 

 the ranges of other species with which it may be 

 associated. 



Vegetation. — When one speaks of the flora or fauna 

 of a region he refers to the actual species inhabiting it, 

 but when he speaks of a forest, prairie, or desert he refers 

 not to the species constituting this assemblage of plants 

 but to the general appearance or aspect of the region. 

 As a matter of fact very different assemblages of species 

 may combine to produce forests of very similar appear- 

 ance. Pine forests occur in Maine, Michigan, and Cali- 

 fornia, for example, which look much alike but which 

 have few species in common, and no one species of pine 

 is found in all. Any of these would have still fewer 

 species identical with a pine forest in Europe or Asia 

 and probably would not have a single species that could 

 be found in a "pine" forest in Chile; in fact the so- 

 called pine forest of the latter would not have even a true 

 pine of any kind but merely another coniferous tree 

 more or less resembling a pine. One would find this same 

 principle to be true of a prairie in the Mississippi Valley 

 compared with one in southern Brazil, or of the deserts 

 of our arid Southwest and the Sahara. 



Illustrations of this sort might be multiplied to almost 

 any extent to illustrate the important fact that similar 

 habitats in any part of the world are occupied by a simi- 

 lar type of vegetation, but that the species are different 

 and in general more different the further removed from 

 one another are the regions under consideration. Thus 

 it is to be understood that terms such as forest, desert, 

 prairie refer to vegetation types without reference to the 



