NORTHRUP, KING & CO'S KINGSCROST HYBRID SEED CORN 
INBRED A 
DETASSELED 
INBRED B 
POLLEN 
INBRED C 
DETASSELED 
INBRED D 
POLLEN 
First year, the four inbred strains are increased in nursery rows of 
15 to 30 plants by hand pollination with the silks and tassels all covered 
with bags. 
Second year, these inbreds are increased in larger volume, usually 
1 or 2,000, also by hand pollination. 
Third year, two single crosses are produced by crossing strain 1 with 
strain 2, and strain 3 with strain 4 in plots well isolated from other corn. 
The two strains which are to be crossed are planted in alternate 
rows. All tassels are pulled out of one strain before any pollen ripens. 
The only pollen in the plot is from the other strain which fertilizes the 
detasseled strain and, therefore, the single crossed seed is produced on 
the strain which was detasseled. 
Fourth year, the two single crosses are planted in large production 
fields in alternate rows. Usually one row of one single cross to three rows 
of the other. The triple rows are detasseled and the tassels on the single 
rows remain to produce pollen to fertilize the detasseled rows. 
Therefore, seed produced on the detasseled rows is double crossed, seed 
being grown on one single cross and fertilized by another single cross. 
It is evident from this that hybrid seed corn is very expensive to 
breed to start with. Production of hybrid seed also is far more expensive 
than seed of the regular varieties. 
Moreover, unless each step in hybrid seed production is very carefully 
handled, the productive 
first year cross inbred parent strains it ability of the hybrid 
seed is materially re¬ 
duced. For instance, in 
the production of the 
double crossed seed, if 
any pollen on the rows 
supposed to be detasseled 
is allowed to ripen and 
fertilizes some of the de¬ 
tasseled plants, seed from 
such plants is not double 
crossed but an increase 
or second generation of 
the single cross. Such 
seed yields very low and 
produces runty plants in 
place of the vigorous, 
high yielding plants 
which the double crossed 
seed should produce. 
A considerable amount 
of experience is essential 
to avoid mistakes which 
reduce the yielding abil¬ 
ity of the hybrid. 
A good hybrid can be 
_ , , . , ... ruined by inexperienced 
Ear chart showing method or breeding hybrid seed corn—and the . 
relative appearance of inbreds, single cross and double cross ears producers. 
Y 
SINGLE CROSS A x B 
T 
DETASSELED 
SINGLE CROSS C x D 
POLLEN 
- V - 
(B x A) x (C x D) 
i 
PRODUCES KINGSCROST HYBRID 
4 TYPICAL EARS BELOW 
I 
v 
— 3 — 
