NQRTHRUP, KING & CO'S KINGSCRQST HYBRID SEED CORN 
Kingscrost Hybrid Seed Corn 
Kingscrost is the brand name which distinguishes our Hybrid Seed 
Corn. It is registered in the U. S. Patent office and can be used only by 
Northrup, King & Co. as a brand for hybrid seed corn. 
Hybrid seed corn is a first generation cross between inbred strains. 
Inbred Strains are developed by continual inbreeding of selected plants 
for several generations. By inbreeding is meant fertilizing the silk with 
pollen from the same plant. 
The development of inbred strains and finding superior crossing com¬ 
binations between them, requires over 10 years. The beginning is made 
with a very large number of selected plants because so many develop 
glaring abnormalities or weaknesses after a few years of inbreeding that 
they must be discarded. 
After 5 or 6 years of inbreeding, a relatively few inbred strains are 
left after a large number of plants have been discarded. Those considered 
satisfactory at that stage are very uniform in all characters, but each 
one is quite different from all the others. 
After inbred strains 
are developed, the next 
step is to discover which 
inbreds, when they are 
crossed together, will 
produce higher yields 
than the corn from which 
they were derived. This 
requires making a very 
large number of crosses 
and comparing them for 
yield with the ordinary 
varieties. Only a few 
such crosses are superior. 
With this information, 
double and three way 
crosses are tried. 
A double cross is be¬ 
tween two single crosses 
involving 4 inbreds. A 
3 way cross is between 
an inbred and a single 
cross involving three in¬ 
breds. A single cross is 
between 2 inbreds. 
After a superior dou¬ 
ble or three way cross is 
discovered, commercial 
production of hybrid seed 
corn is possible. Most 
commercial hybrids are 
double crosses which re¬ 
quire four years to grow. 
FIRST YEAR CROSS INBRED PARENT STRAINS 
DETASSELED DETASSELED 
INBRED A INBRED B 
~Y- 
DETASSELED 
fRO* 
INBRED C 
INBRED 
-V" 
CiD 
Method of crossing inbred plants and the resulting single 
crosses to produce double cross hybrid plants 
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