Geographical Distribution 187 



throw upon the great questions of evolution, adaptation and 

 the vicissitudes and changes of plants and animals in the 

 past. But apart from this purely "theoretical" interest they 

 have an important bearing upon human life today, for they 

 give us a clue to the suitability of any region for crops of a 

 given type. Thus if a settler in a given region wishes to 

 know what kind of crops will grow best in his region, it is 

 essential for him to know, not only the character of the soil 

 in his area and the amount of rainfall, temperature range, 

 etc., but the type of plants which will grow well in that par- 

 ticular climate, or in other words the life zone in which his 

 area lies. To make this information available to our farmers 

 the Biological Survey has prepared a life zone map of the 

 United States and Canada, together with a list of the various 

 cereals, fruits and vegetables best adapted to each zone. 



Thus does the biologist seek to make his knowledge "prac- 

 tical" in the rendering of service to the world. 



