When the plant apical meristem cells interpret the combination of daylight length and accumulated heat, as determined by genetics, the terminal shoot meristem and at least one of the meristems located at a stem nodes, begins to produce cells for the tassel and shoot. Resulting modified stems and leaves now produce the male and female flowers of the corn plant.
Maize male and female flowers are on separate branches of the corn plant, thus the species is called monoecious, as opposed to the dioecious flowers of soybeans. Both the ear-forming branch and the terminal tassel is composed of multiple flowers. Each kernel that forms in the ear traces to a single flower with a single ovule within the fruit wall, the ovary. Both male and female flowers of corn begin as dioecious but the male portion in the ear and the female flower in the tassel are aborted very early in the development of each. A mutation or an environmental factor can overcome the abortion, resulting in tassel seed or terminal tassel on an ear.
A corn tassel may include up to 1000 spikelets, each one including 2 florets. These individual flowers are enclosed in the modified leaves called glumes. Each of the florets have three stamens, consisting of filaments and anthers. Each anther includes multiple cells called microspore mother cells or microsporangia. Meiosis occurs in these diploid cells resulting in 4 haploid microspores per mother cell. This occurs over a period of 3 days. Microspores become free of each other as they grow for a few more days. The individual haploid nucleus in each microspore undergoes mitosis, resulting in two haploid cells within the individual pollen grain. The pollen grain secretes a pollen wall within another 7 days. Starch crystals accumulate within the pollen grain during that wall formation period as the cytoplasm of the pollen grain dehydrates. A small pore is formed in the pollen wall.
Pressure from the growing pollen grains and dehydration of anther walls causes the split that allows the release of pollen grains. One thousand spikelets each with 2 florets with three anthers each with hundreds of pollen grains easily produces a cloud pollen. Production of the spikelets over a period of days results in daily release. Pollen longevity may only be a few hours in high heat but the release over consecutive days in a field of corn usually assures viable pollen reaching most viable female stigma.
The remarkable human selection and development of maize adapted to multiple environments because of available genetic diversity is largely due to the separation of male and female flowers. (Corn Journal 7/17/18)
About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.