UNITED STATES DEPARTMENT OF AGRICULTURE 
In cooperation with the 
Tennessee Agricultural Experiment Station 
DEPARTMENT BULLETIN No. 1354 
Washington, D. C. ▼ December, 1925 
THE PRODUCTIVENESS OF SUCCESSIVE GENERATIONS OF SELF-FERTILIZED 
LINES OF CORN AND OF CROSSES BETWEEN THEM » 
By Frederick D. Richey, Agronomist in Charge of Corn Investigations, and 
L. S. Mayer, Assistant Agronomist, Office of Cereal Investigations, Bureau of 
Plant Industry 
CONTENTS 
Page j Page 
Basis for the investigation.. 1 i Determining the value of individual lines 
The comparison of successive generations 2 J for crossing—Continued. 
Growing seed for comparison 2 Method of comparison 11 
Method of comparison 2 Experimental data 11 
' Experimental data... 3 Discussion 15 
Determining the value of individual lines Summary 17 
for crossing 10 ! Literature cited 18 
Obtaining the crossed seed 10 t 
BASIS FOR THE INVESTIGATION 
It has long been recognized that too close breeding causes a de- 
creased productiveness in corn and that crossing varieties tends 
frequently to result in increased vigor and yield. On the basis of 
this knowledge some of the older methods of corn breeding were 
planned carefully to avoid possible inbreeding and some to utilize 
the vigor of first-generation crosses between varieties. The Mende- 
lian interpretation of hybrid vigor, as due to the complementary 
action of dominant favorable growth factors, gave a plausible explana- 
tion of the phenomena of inbreeding and crossbreeding. The general 
acceptance of this interpretation has caused an extensive revision of 
corn-breeding methods. It is recognized that maintaining a high 
degree of hybridity only prevents the expression of unfavorable 
recessive factors without eliminating them. The newer methods 
therefore seek to bring these unfavorable factors into expression, 
where they may be recognized and eliminated. This involves selec- 
tion within self -fertilized lines as the first step. 
A study of the possibility of obtaining larger yields of corn by 
methods involving selection within self -fertilized lines was begun 
among the plants of the F 2 generation of the cross Whatley X St. 
1 The breeding plats from which the strains used in these experiments were obtained were conducted 
by the senior writer in cooperation with Lee Wilson & "Co., Armorel, Ark., in 1916, 1917, and 1918 and 
the Burdette Plantation, Burdette, Ark., in 1919, 1920, and 1921. The senior writer also is responsible 
for the self and cross pollinations made at the Arlington Experiment Farm in 1921, for the preparation of 
this seed for planting, and for the general plan of the experiment. The breeding plats in 1922 and sub- 
sequent years and the yield experiments in 1922 and 1923 were located at Knoxville, Tenn., in cooperation 
with the Tennessee Agricultural Experiment Station and .under the supervision of the junior writer. The 
writers wish to express their appreciation of the assistance rendered by S. H. Essary, of the Tennessee 
Agricultural Experiment Station, during the progress of the experiments at Knoxville. 
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