10 Nebraska Experiment Station Research Bulletin 19 
A distinction must be made between these adaptive changes 
and mere temporary growth response. Hereditary character 
changes in corn may occur by: (1) Mutation from an indi- 
vidual, thus producing a new character; (2) Mendelian recombi- 
Fig. 1 — A typical field of corn in western Nebraska. 
nation of unit characters resulting in new forms: and (3) segre- 
gation of the more suitable types present in a mixed population. 
Since the crop environment of any locality is necessarily 
somewhat fluctuating or variable from year to year, important 
crop adaptation characteristics are congenial for the most part 
to the mean or normal conditions. A crop can not be in full 
accord every year with a fluctuating environment. Conse- 
quently, a crop to be well adapted from an agricultural stand- 
point must be capable of some adjustment to variable conditions. 
Adaptation occurs as a favorable reaction to some one or 
more growth factors of the environment. The environmental 
conditions which are apt to become limiting factors in Xe- 
