Corn Confidentials

By Eve Pranis

Corn, called mahiz by the first Americans who met Columbus, and known by much of the world as maize, is known today by the botanical name Zea mays. Like other grass family members, corn is a monocot, having only one cotyledon or seed leaf. Invite your students to observe how corn as a monocot differs from a dicot (beans, for instance), by soaking both corn and beans overnight, then dissecting each type of seed.

Students may initially notice that a soaked bean seed will easily split apart, while a corn seed will not. If they split the corn seed in half lengthwise with scissors, they should discover that, like the bean seed, a corn seed also has a tiny embryo. Unlike the bean seed, which has who large seed leaves packed with food (cotyledons), the corn seed has only one small cotyledon. In monocots, the food for the young plant is stored in the endosperm that surrounds the embryo. The small corn cotyledon, which is part of the embryo, absorbs food from the endosperm as it grows. The quality of the endosperm helps us classify corn into major types, ranging from the hard, starchy endosperm in popcorn to the soft, sugary endosperm of sweet corn.

As your students closely examine the seeds, then observe how both corn and beans germinate, emerge from the soil, and mature, have then record ways in which corn and beans are similar and different. As it emerges from the soil, for instance, a bean is curved, thus protecting the cotyledons from breaking as they emerge from the soil. The corn's protective sheath, on the other hand, penetrates the soil like a spear, covering the fragile leaves inside.

If students carefully observe and compare leaves, they should notice that the corn, as a monocot, has parallel veins, while beans have branching veins. You might eventually assess students' understanding and observation skills by having them observe other types of seeds and seedlings and classify them as monocots or dicots.

Gone with the Wind

If you ask your students whether they've ever seen flowers on a corn plant, you may get mixed responses. If you have the opportunity to grow corn to maturity outdoors, either in the garden or in containers outside the school, students will be able to observe corn flowers, and may even be able to play at being "pollinators!" As with other grasses, corn pollen is carried by the wind rather than bees or other pollinators, so its flowers have not evolved with bright colors, aromas, and other adaptations to attract pollinators. Corn plants contain both male and female flowers in different locations on the plant. An ear of corn is actually a female flower stalk, resting between the sheaths of the leaf and stem. The only part of the female flower that we see when the plant is growing are the fine hairs called silks. These are actually tubes through which pollen will travel when released from the male flower or tassel that branches at the top of the plant.

Wind carries pollen from the tassels of some corn plants to silks on others. Each fertilized strand of silk develops into a single kernel with characteristics of both parents.

If your students have studied seed dispersal, you might ask them to infer how corn seeds are dispersed naturally. Domesticated corn actually has no successful seed-dispersal mechanism, but is totally dependent on humans to reseed. Students may want to experiment to see what might happen if an ear of corn, wrapped tightly in a husk, fell from the plant. (Even if the kernels could germinate, they would compete with each other for resources and die.)

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