MadSci Network: Botany

Re: How many ears of corn grow on one stalk?

Date: Thu Jun 15 10:15:39 2000
Posted By: Joseph E. Armstrong, Faculty, Botany, Illinois State University
Area of science: Botany
ID: 959714050.Bt

This question makes me wonder if people are beginning to rely upon the WWW 
as they used to rely upon scriptural authority, as a source of answers for 
questions they could answer themselves just by looking.  
However, perhaps I misinterpret the question.  Like all traits, the number 
of ears on a stalk of corn is subject to some variation.  An ear of corn is 
an inflorescence, a lateral stem or branch modified to bear flowers, and in 
the case of maize (the preferable common name because "corn" only means 
common grain of the region; "corn" in Scotland = oats) only female flowers. 
 Each kernel is a 1-seeded fruit representing a single flower.  A long 
slender style & stigma attached to each flower extends outside the 
surrounding bracts, the husks, and altogether they are called silk. The 
tassel on top of the stalk is an inflorescence of male or pollen-producing 

Each stalk of maize will bear only 1 tassel, but an ear could form 
associated with each of several leaves (branches always form above the 
point a leaf attaches to the stem).  So maize can have one to several ears. 
 Genetically uniform field corn usually only has a single ear per stalk.  
Most sweet corn varieties will produce 2-4 ears per stalk, and one variety, 
called "six-shooter", appropriately enough produces six ears per stalk, and 
it also grows pretty tall.

The reason most modern hybrid varieties have been selected for fewer ears 
deals with two issues, pollination and investment in offspring.  Like many 
plants maize flowers develop from the bottom toward the top.  Only those 
ears mature at the time the tassel matures and releases pollen will be 
pollinated.  So ears can mature too early or too late.  This is not a 
problem in a natural population with some mixes in ages and some variation 
in flowering time, but in crop  fields all the individuals are within one 
or two days of the same age, so there aren't enough individuals producing 
pollen early and late to pollinate early or late ears. So breeders have 
selected for varieties only producing one or a few ears to assure 
pollination during the brief few days the tassel matures. 

The second reason for only having one or a few ears is that the plant only 
has a limited amount of resources for producing offspring.  So if limited 
resources are shared among many offspring, they will be smaller.  If shared 
only among a limited number of offspring, they will be bigger.  Field corn 
may only produce one ear, but it's a big ear with many flowers and the 
kernels are big too.  So there may be no particular advantage in terms of 
production of offspring in having more ears.  

Teosinte, the wild ancestor of maize, is a typical multistalked grass.  It 
produces numerous small heads of 6-kernels each, and each branch is 
terminated by a tassel of pollen flowers.  Domestic maize with no branches 
and fewer ears increases the investment made in each kernel, so bigger ears 
are possible bearing many flowers maturing into bigger kernels. 

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