Making Southern Hybrids Out of Inbreds 
PRODUCING A FOUR-WAY CROSS 
Pure Inbred Strains 
The next step is to cross these inbreds. The result is as astonishing 
as touching a match to gunpowder. For some reason that scientists 
have not yet fully explained, when one puny little inbred is mated to 
another the offspring grown from that seed is astoundingly strong, 
large and vigorous. Something happens when the germ plasms from 
two different purebred strains are brought together that 
produces a degree of vigor which no one has ever been able 
to secure in any other way. 
Something else happens, too. The offspring may combine 
the desirable characters of both parents, with the unde¬ 
sirable characters submerged; or some of the undesir¬ 
able characters may be so prominent that the cross is 
of no value. Some crosses “nick.” Some don’t. 
So one hybrid is crossed with another, then the 
seed tested in the field until the breeder knows 
which crosses are good and which ones are not. 
When one inbred is crossed with another it is 
known as a single cross. Until more vigorous and 
high-yielding inbreds are developed, the yield from 
many hybrids is so small that the seed is very 
expensive. 
So the corn breeder takes two single crosses, 
which tests have shown to be good, and crosses 
them. Again some of these double crosses, which 
are a combination of four inbred parents, are dis¬ 
carded because of some undesirable features. But 
by the tedious process of trial and error the breeder 
finally gets a corn plant which combines yielding 
ability, strong roots, stiff stalk and high quality 
ear with that mysterious vigor which results from 
hybridization. 
Then he has a useful hybrid, ready to be pro¬ 
duced on a large scale and sold as commercial 
hybrid seed. And he can always be sure of giving 
his customers exactly the same thing, because the 
same combination of inbreds crossed in the same 
way will always give the same result. 
SINGLE CROSS 
C 
Detasseled 
Produces 
D 
Furnishes 
Pollen 
single" CROSS 
(B x A) x (C x D) PRODUCES 
Represents ear of a commercial crop produced from hybrid seed 
Inbreeding or "selfing" is accomplished by dusting 
the pollen of a corn plant on its own silks 
After the inbred recipe is established, three 
more years are required to produce Southern 
Hybrid seed commercially. The work of in- 
breeding and “selfing” and the production of 
southern hybrids on a small scale is done all in 
one field by controlling the pollenization with 
silk and tassel bags. 
To produce southern hybrids on a large scale 
the inbreds are first brought up to a commercial 
scale by planting in isolated blocks a long 
distance from other corns; then the two inbreds 
which are to comprise each single cross are 
planted in an isolated field in such a manner 
that the entire field is planted in a ratio of 
one row of male plants to three or four rows of 
female plants. Just before the silks emerge 
the tassels—which are the male portion of the 
plant—are removed from the female rows. The 
silks of those rows therefore receive pollen 
only from the male row which still carries its 
tassels. Thus a cross is effected between the 
two kinds of corn. As before stated, this work 
of producing single crosses must be carried on 
in different fields as only one single cross can 
be produced in any given field. The following 
year the two single crosses are crossed together 
and the seed is again saved from the female 
rows. It is this seed which is brought in, dried, 
carefully graded and processed to be used later 
for planting. 
Green Ink List Enclosed 
RUSSELL-HECKLE 3 
