INCREASING THE SUPPLY OF PARENT CORN the third step 
AFTER NEW PIONEER HYBRIDS demonstrate and i)rove their 
•• superiority throughout tlie testing period wliirh lasts from three to 
five years, they are ready for rommeriral production. 
But before a new hybrid can he produced on a large scale, an 
increase must he made on the supply of seed for the inhreds which 
make up its parentage. 
To protect the plots from foreign pollen, each of the four original 
inbred strains is planted in isolated fields located 4(( or more rods 
from the nearest cornfield. 
The seed harvested from the four fields is used to plant the four 
iidireds we will call A, B, C and 1). These are then cross-bred in i)airs 
to produce two “single crosses.” 
To produce a “single cross,” PIONEER corn breeders alternate one 
row of Inbred A (male) with two rows of Inbred B (female) all 
through a field. The female is detasseled to prevent self-pollination. 
The pollen from the tassels of male Inbred A cross-pollinates the silks 
of female Inbred B. 
Inhreds C (male) and U (female) are hybridized in the same man¬ 
ner. Seed picked from female rows B and D grows two different 
“single crosses” wdiich are then crossed to make the final “four-way” 
hybrid cross. 
Top—A FIELD SHOWING TWO STRAINS OF INBREDS, A AND B, BEING CROSSED 
Bottom—A CROSSING FIELD OF TWO OTHER STRAINS OF INBREDS, C AND D 
