CORN BREEDING 6 
nally, half going to each of the two new daughter cells. All of the 
body cells of a plant therefore contain the same number of chro- 
mosomes. Half of these were derived from the male parent and 
half from the female parent of the plant at the time fertilization 
initiated the development of the seed from which the plant has 
grown. 
With certain exceptions which need not be considered here, the 
number of chromosomes in the body cells is constant for each kind 
of plant or animal, the number in corn usually being 20. 
As the time for reproduction approaches, certain cells in the 
reproductive parts of the corn plant divide in a different manner. 
The chromosomes become paired at this stage, one of each pair hav- 
ing come from the male and the other from the female parent of 
the plant. One chromosome from each pair, without reference to 
parentage, goes to one of the daughter cells, while the corresponding 
chromosome of each pair goes to the other. This gives rise to two 
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Fig. 1. — Diagram showing cell division, including both somatic (body) cell and repro- 
ductive cell formation 
cells, each having half of the number of chromosomes found in the 
body cells. Because of the reduction in the number of chromosomes 
resulting from it, this is called the reduction division. Following 
this these cells again divide, each chromosome dividing longitudi- 
nally and half going to each daughter cell. The resulting cells, 
each with 10 chromosomes, are the so-called microspores or mega- 
spores, as the case may be. The male sexual cells are derived from the 
microspores, and the eggs (female sexual cells) are derived from the 
megaspores. The steps in the formation of body and sexual cells 
in an organism having two pairs of chromosomes are indicated dia- 
grammatically in Figure 1, one pair of chromosomes being shown as 
black and the other as crossbarred. 
Every normal corn plant produces both male and female sexual 
cells. The former are produced in the tassel, or staminate inflores- 
cence (pi. 2), and the latter in the ear shoot, or pistillate inflorescence 
(pi. 3). 
