20 Nebraska Agricultural Exp. Station, Research Bui. 20 
Fig. 1 . — Average dates of the last killing frost in the spring and the 
first killing frost in autumn for various regions of Nebraska. The 
hereditary type of corn grown in different regions should vary in 
order to fit the length of frost free period available for growth. 
ft can annua/ precipitation. 
'Isotherms for corn season of flay, June, July, August. 
O Sources of seed for test recorded in table Z. 
Fig. 2. — Average annual precipitation and normal isotherms for the corn 
growing season of May, .June, July, and August. The hereditary 
type of corn grown in different regions should vary in accordance 
with the precipitation and heat units available for growth. 
