16 
Nebraska Agricultural Exp. Station , Research Bui. 20 
Many of the problems investigated in these experiments 
have been studied elsewhere by other workers, 1 with varied re- 
sults and conclusions. One probable cause for this diversity of 
results from certain selection and breeding practices is the use, 
by different investigators, of varieties differing in their degree 
of local adaptation. It is reasonable that a poorly adapted 
variety is more likely to respond favorably to selection and 
breeding than is a well-adapted variety. The process of im- 
provement in such a case may simply be that of directed ac- 
climatization. This diversity of results is doubtless also to be 
accounted for, in part, by experimental errors which have un- 
consciously modified the correct indications. Method studies, 
such as reported in Nebraska Agricultural Experiment Station 
Research Bulletin No. 13, indicate many sources of possible 
error. These chiefly arise from irregularities in stand and soil, 
insufficient numbers of individuals and replications of plats, 
competition with adjacent unlike sorts, and insufficient duration 
of tests. 
Some experiments are greatly subject to seasonal effects and 
require continuation thru a period of years in order to secure 
average indications. The nature of other experiments is such 
that the seasonal variation is not a vital factor, and dependable 
indications may be had in a much shorter time, provided the 
number of replications is ample and the method employed is 
correct. 
ECONOMIC CONSIDERATIONS 
The United States produces, in round numbers, 3,000,000,000 
bushels of corn annually. Nebraska’s normal corn crop ap- 
proaches 200,000,000 bushels. (Table 1.) An increase in the 
acre yields accompanied by an improvement in or at least main- 
tenance of commercial quality would be a matter of no small 
moment. The significance of improvement along these lines, 
even tho slight, is so profound that agricultural agencies seem 
justified in the expenditure of great effort to establish the essen- 
tial considerations in such improvement. An annual increase of 
approximately seven million bushels in Nebraska’s corn crop 
would result from increasing the average yield one bushel per 
acre. 
The literature bearing upon many of the problems investigated herein is 
so extensive that it has seemed expedient to completely omit all literature 
citations. 
