THE CLIMATE OF MICHIGAN. 



705 



^^Ke SuPef?ioR 



CHART XIII. -length of growing season, in days. 



PART III. 



THE RELATION OF THE CLIMATE OF MICHIGAN TO AGRICULTURE. 



Climate 'and agriculture are closely related because all crops require 

 certain amounts of heat, moisture and sunshine to make normal growths. 

 The exact requirements of any crop for any given climatic condition are 

 very difficult to determine and state in figures, because the relationship 

 is complicated and plants are able in a measure to overcome unfavorable 

 environment. Probably no exact statement has yet been made as to the 

 most favorable temperature conditions, for example, under which a 

 crop Avould tlirive best, oi" liow many lieat units are necessar}^ for any 

 crop plant to perform its life functions to the best advantage. There 

 have been numerous attempts to find a "thermal constant," as it has 

 89 



