Corn, or maize, is a monoecious plant, possessing both male and female reproductive structures—separate flowers—on the same individual. This arrangement facilitates reproduction and the development of kernels. Understanding the function of these parts provides insight into corn development.
The Male Flower: Anatomy and Role of the Tassel
The male flower is the tassel, the large, branched structure situated at the top of the stalk. It is the first reproductive part to emerge, typically appearing shortly before the female flowers are ready. The tassel consists of a central stalk and lateral branches containing spikelets that house the pollen-producing organs.
Each tassel holds thousands of anthers, which contain the pollen grains. A single tassel can produce between two and five million pollen grains, ensuring a large supply. Pollen release, known as anthesis, often begins near the center and progresses outward, sometimes lasting five to eight days.
Corn is a wind-pollinated plant, maximizing dispersal. The anthers open up, releasing a fine, yellowish powder that drifts on air currents, shedding most heavily in the morning. While the pollen is heavy and falls quickly, the wind can carry it over short distances.
The Female Flower: Structure and Function of the Ear and Silk
The female flower is the ear, which develops from a shoot lower on the stalk, encased in protective outer leaves called husks. Inside the husk, the ear consists of a cob covered with rows of ovules. Each ovule is connected to an individual, elongated strand known as a silk.
The silks are the receptive surface of the female flower, acting as the stigma and style. These structures emerge in a bundle from the husk tip, creating a target for falling pollen. The surface of the silk is covered in small, sticky hairs designed to capture airborne pollen grains. Since silk elongation begins from the base of the ear and progresses toward the tip, the silks connected to the base kernels emerge first.
A single ear can contain up to 1,000 ovules, requiring an equal number of silks to receive pollen. If successfully pollinated, each silk guides the male genetic material to its corresponding ovule, which develops into a kernel. The appearance of fresh, moist silks signals that the female flower is receptive and ready for fertilization.
The Process of Corn Pollination
The reproductive cycle integrates the male and female parts through a carefully timed process. The successful development of a full ear depends on the synchronization, or “nick,” between the release of pollen from the tassel and the emergence of receptive silks. Silks typically emerge and are ready to receive pollen shortly after the tassel begins shedding.
When a pollen grain lands on a receptive silk, it germinates almost immediately. The grain then produces a pollen tube, which grows down the hollow channel of the silk toward the ovule at the base. This journey delivers the male genetic material, resulting in the fertilization of the ovule, which usually occurs within 12 to 28 hours after the pollen lands. Once an ovule is fertilized, the silk connected to it detaches and begins to dry out and turn brown, signaling a successful union.
A lack of synchronization between tasseling and silking can lead to poor fertilization. Environmental stresses like severe drought or high heat can delay silk emergence while accelerating pollen shed, causing the pollen to be gone before all silks are ready. When a silk is not pollinated, its ovule fails to develop, resulting in missing kernels, often noticeable as blank spaces or “tip blanking” on the cob.