156 THE GEOGRAPHICAL DISTKIBUTION 



fruit, in a certain soil and, under certain definite conditions 

 of heat, light, and moisture. In this respect the animal 

 and vegetable world are governed by the same laws. 



Soil exercises a marked influence on the geographical 

 distribution of species. It is impossible to examine the 

 flora or fauna of any country without arriving at this con- 

 clusion. The mountains and the valleys, the margin of 

 rivers and the shores of the ocean have all their appro- 

 priate vegetable and animal forms. When we burn a 

 plant, the materials attracted from the earth and atmo- 

 sphere and blended together in its organism are separated, 

 and we restore to the atmosphere the gaseous part of 

 the plant which was taken from it, isolating the mine- 

 ral matter derived from the soil under the form of 

 the incombustible ash which remains. Now the small 

 amount of ash left, proves that the atmosphere is the chief 

 source of .vegetable nutrition; yet nevertheless its import- 

 ance is not on this^ account to ba underrated. This ash 

 does not enter the organism of the plant mechanically 

 along with the fluid matters absorbed by the roots from 

 the soil, for analysis has proved that its chemical composi^ 

 sition varies in different plants. Therefore, each nucleus 

 of cells which forms the substance of the germinating seed, 

 must exercise a special attraction on certain inorganic ele- - 

 ments, which it separates from the other mineral matters, in 

 the midst of which it grows, and which inorganic elements 

 are absolutely necessary to the healthy evolution of the 

 embryo which it encloses. Plants are therefore unques- 

 tionably influenced in their localization, by certain peculiar 

 inorganic elements which they derive from the soils in 

 which they grow. 



When the soil is of such a nature as to favor the growth 

 of one particular species more than another, it becomes 



