64 



CORN CROPS 

 TABLE XII 



It is apparent from the above data that up to 70 degrees 

 north latitude there is sufficient sunshine during the 

 summer months to produce corn, were it not for other 

 limiting factors, as low temperature due to a. cold soil and 

 cold air currents. 



The data presented thus far are on the basis of per- 

 fectly clear days, but the presence of clouds reduces the 

 sunshine. At Montsoris, France, careful records for the 

 corn-growing season kept from 1875 to 1885 showed 

 only about 40 per cent of the possible intensity of sunshine, 

 due to cloudiness. Corn under such conditions does not 

 grow well, but requires, even at that latitude, what might 

 be termed a rather " sunny " climate. 



We may conclude that except where cloudiness prevails 

 for half the time, there is sufficient sunshine for corn pro- 

 duction even up to 70 degrees latitude. 



50. Relation of rainfall to growth. — The transpiration 

 of 14 to 20 tons of water is required to produce one bushel 



