|MadSci Network: Botany|
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 flowers. 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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