LIST OF ILLUSTRATIONS 



Page 



Physical Features of North America Frontispiece 



Precipitation Zones of the World - - - - 3 

 Map Showing the Northern Limits of some 



crops and trees - - 7 



Nature's Map of the Prairie Provinces^ - - 8 



Precipitation Zones in Canada 14 



Average Annual Precipitation 15 



Monthly Distribution of Precipitation in 



Canada -- 16 



Monthly Distribution of Precipitation at 



Different Representative Points - - - - 17 



Precipitation at Swift Current, Sask. - - 18 

 Average Depth of Snowfall in Western 



Canada -- 19 



Variations from Normal Precipitation • - 22 

 Temperature Zones of Canada ----- 26 

 Average Temperature by Months at Repre- 

 sentative Points 27 



Frost Free Period at Different Points - - 29- 



Temperature Zones of Canada 31 



Hours of Possible Sunshine Daily in Summer 3") 



Rock Weathering - - - - 39 



Soil Surface Map of Iowa ------ 42 



Pot Cultures - - 47 



Illinois Fertilizer Experiment ----- 59 

 xvii. 



