..-M \ 
UNITED STATES DEPARTMENT OF AGRICULTURE 
DEPARTMENT BULLETIN NO. 1341 
Washington, D. C. 
August, 1925 
EFFECTS OF CONTINUOUS SELECTION FOR EAR TYPE IN CORN ' 
By H. S. Garrison, Assistant Agronomist, and Frederick D. Richey, Agronomist 
in Charge of Corn Investigations, Office of Cereal Investigations, Bureau of 
Plant Industry 
CONTENTS 
Page 
Object of the investigation 1 
Material and methods 2 
Establishing the strains 2 
Growing seed for comparison 2 
Method of comparison 2 
Pago 
Experimental data 3: 
Data on number of kernel rows_ 5 
Data on productiveness 6 
Discussion 7 
Summary 10 
Crosses between commercial varieties of corn frequently have pro- 
duced more in the F^ generation than the average yield of the 
parents and in many cases more than the higher yielding parent. 
This suggests that varieties frequently may be too homozygous to 
permit maximum yields. Such a condition might be caused by an 
accidental narrowing of hereditary lines through the use of too few 
individuals for seed from time to time. It also might be caused^ 
theoreticalh', at least, hj close selection to a particular type; that is^ 
close selection for certain superficial characters would affect pro- 
ductiveness if the genetic factors controlling such characters also 
affected the groAvth of the plant or happened to be linked with fac- 
tors that did affect plant growth. 
OBJECT OF THE INVESTIGATION 
The object of the investigation was (1) to determine to what 
extent and in what length of time strains having distinct character- 
istics could be obtained by mass selection from a well-established 
variety of corn and (2) to determine the relative productiveness of 
the selected strains, of the F^ crosses between them, and of the origi- 
nal varietv. 
1 The selection of the strains used in these experiments was beg-un under the direction! 
of E. B. Brown, formerly Agronomist in the Office of Cereal Investigations, and was con- 
tinued under his supervision through 1921. Most of the selections and records were 
made by him and by J., M. Hammerly, Assistant in Corn Investigations, Office of Cereal 
Investigations, during the earlier years and by the senior writer in tJie later years of the 
experiments. 
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