Maize is among the most widely used plants in the globe. Some may know it as corn. This essay analyses the biology of the plant. It traces its history and the role that it plays in the lives of human beings.
Taxonomy
The scientific name of the maize plant is Zea mays . It belongs to the Poaceae family. The Poaceae family is the grass family. It also belongs to the Andropogonoeae tribe which falls under the Panicoideae. Primarily, it is classified as a monocotyledon, hence the class Liliopsida. It is a flowering plant, hence under Division Magnoliophyta. The maize plant produces seeds, thus falls under the superdivision Spermatophyta. It falls under the subkingdom Tracheobionta, a vascular plant category. (United States Department of Agriculture, 2017)
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The plant has a chromosomal number of 2n = 20. The plant has a basic chromosome A complement. It may contain supernumerary chromosomes known as B chromosomes. These B chromosomes are exceptional and do not pair with A chromosomes during meiosis. The maize genome has a total of 40000 to 56000 genes.
History
The maize plant has been traced to the Mesoamerican region. It is thought to have been somewhere in the Mexican highlands. The discovery of America by Europeans aided in the spread of the cultivation of maize. This took place around the 15 th Century. Domestication of maize is also thought to have taken around this time. As the cultivation of maize has occurred over time, there has been selection of maize varieties. This has been based on farmers’ preference and the prevailing environmental conditions.
The growth of maize has been aided by its ability to thrive in different environments. It thrives in both tropical and temperate environments. From Russia in Europe to Tanzania in Africa, maize thrives in most environments. It thrives at different altitudes, from sea level to 3800 meters above sea level. Its maturing period falls between 42 to 400 days, thus aiding in its survival in these environments.
Morphology
The maize plant is usually 1 – 4 meters tall. It forms a seasonal root system with a culm comprised of nodes and internodes. Some plants have elongated lateral branches called tillers. Many temperate plants are shorter than the tropical varieties.
The leaves are usually broad. A single leaf develops at each node in opposite ranks. This arrangement is termed distichous. A mature maize plant usually has 30 leaves. Tropical varieties develop more leaves than the temperate varieties. Each leaf usually consists of a sheath surrounding the stalk. An expanded blade is connected to the sheath by a collar.
In cross-sections of the stalk, the outermost layer that can be viewed is the epidermis. Layers of sclerenchyma tissue serve to enhance the strength of the stalk. Vascular bundles are scattered throughout the parenchyma. The bundle sheath cells have a higher number of chloroplasts than mesophyll cells. The chloroplasts are also larger. The increase in size and number of chloroplasts aids in the utilization of carbon dioxide by the plant (Australian Government Department of Health and Ageing, 2008) .
Maize is a monoecious plant. The lateral branches terminate in an ear, which is the female part. The tassel is found at the top of the stem. It develops from the apical meristem. It is made up of a central spike and several lateral branches. This is the male part. The ear is surrounded by leaves called husks. The husk serves to offer protection to the developing ear. On maturity, the husks protect the grains from pests such as birds and insects. The cob, the axis of the ear, has between 4 to 30 rows. These rows consist of ovaries each containing an ovule. The ovules that will develop are 300 to 1000 in number. The silks develop from the style canals of the ovaries.
Development
Reproduction of the maize plant can either be sexual or asexual. In the early phases of growth, the male and female inflorescences contain both male and female parts. As the plant matures, the stamen degenerate in the axillary inflorescences. The same process is experienced by the gynoecia in the apical inflorescence.
The apical meristem undergoes elongation. It develops into the tassel. The tassel sheds pollen continuously for a week. The female inflorescences develop from axillary buds. The flowers are borne in rows. The ovules and flowers develop from the base upwards (acropetal). A style elongates from each flower towards the tip of the cob. This results in the formation of silks. The silks develop over 3 to 5 days. They can grow past 30 cm in length. The silks contain trichomes. They form an angle with the style and help in holding pollen grains. The silks that are receptive are usually moist and sticky. The anthers usually mature before the gynoecium. The anthers start shedding pollen grains 2 or 3 days before the silk emerges from the husks. The gynoecium has usually matured before the emergence of the silk. (Australian Government Department of Health and Ageing, 2008)
Maize pollen is larger compared to other pollen. Most pollen lose their viability within 2 hours of exposure to the atmosphere. Humidity plays a key role in its viability. Pollen has a higher viability at higher levels of humidity. Fresh pollen is white and spherical. Non-viable pollen is yellow and collapsed. Pollination in the maize plant can either be cross-pollination or self-pollination. Self-pollination accounts for 5 percent of the pollination. Insect pollination has not been recorded on maize plants. In cross-pollination, pollen grains are released in the mid-morning. They are then shed continuously for 1 to 3 days. The plant, as a whole, produces pollen for 14 days. Thermal and air turbulence may extend the dispersal distances of pollen. The horizontal spread occurs at a rate of 21-32 cm per second. The level of dehydration of pollen affects its rate of dispersal.
On landing on the silk, the pollen begins to germinate. It takes up to 24 hours for the pollen tube to reach the ovule (Kapu & Cosgrove, 2010) . After fertilization, the silk dries up and detaches from the ovary. Embryogenesis occurs resulting in the development of leaf and root primordia. These are invested by a scutellum. The fruit of the maize plant is a caryopsis, a single- seeded fruit. The pericarp and the seed coat are fused and form the fruit wall. This is why the seed and the fruit appear the same. For what is actually the fruit, we unwittingly tend to call it the seed. The maize kernels are made up of the embryo, endosperm and the fruit wall. After silking, the maize plant typically matures within 55 to 65 days.
Uses
The plant has a wide range of uses. It can be used at the various developmental stages from baby corn to mature grain. Maize is used as a stock feed. It is fed to animals as silage, grain, dry forage or green chop. Some by-products of the milling process such as maize bran are also used as animal feeds.
Processed maize can be used as an ingredient in foods and drinks. These forms include corn syrup, maize meal et cetera. Corn starch is fermented to produce alcohol. Corn oil is a by-product of starch production. It is used in food manufacturing. Over the years, different types of maize have been developed depending on their intended uses.
Maize is the prime source of starch in the world. As civilizations have emerged and disappeared, its uses have formed a backbone of these societies.
References
Australian Government Department of Health and Ageing. (2008). The Biology of Zea mays.
Kapu, S. N., & Cosgrove, D. (2010). Changes in growth and cell wall extensibility of maize silks following pollination. Journal of Experimental Botany , 4097-4107.
United States Department of Agriculture. (2017). Classification . Retrieved from United States Department of Agriculture: https://plants.usda.gov/java/ClassificationServlet?source=display&classid=ZEMA
