The maize plant is monoecious, bearing male flowers in the tassel and female flowers on the lateral ear shoots of the same plant.

Tassels. Approximately 30 days after sowing, when the stem is only 2 cm long and the plant just knee-high, the tassel is initiated. At this stage, the growing point switches from producing leaves to producing the terminal reproductive structure, the tassel.

Approximately 50 days after germination and several days before pollen-shed, the top internodes elongate and the tassel emerges from the leaf whorl (Figure 10). The maize plant reaches the VT growth stage when the last branch of the tassel is completely visible.

Pollen is produced in the male spikelets of the tassel. Each spikelet consists of a pair of flowers (florets) enclosed in two large glumes (Figure 11). The florets contain stamens that produce the pollen grains.

Anthers and filaments make up the stamens. Under favorable conditions, the anthers emerge; generally mid-morning. Anthers break open at the tips, resulting in pollen-shed (anthesis; Figure 10).

Anthesis (R0) is a useful growth stage to observe, because it marks the transition to the reproductive phase, and is less sensitive to environmental factors than silking (R1).

The pollen does not usually move far unless there is adequate wind to promote cross fertilization. In unfavorable conditions (for example, very high temperatures or cold, rainy weather), there may be no pollen-shed.

The first spikelets to open and shed pollen are those on the central axis of the tassel. Usually, pollen shed continues in both directions from the central spikelets to both ends of the tassel.

The last spikelets to shed pollen are those at the base of the tassel. Most tassels shed pollen for 5–8 days, with pollen production reaching a peak around the third day.

A vigorous maize plant can produce 25 million pollen grains, so quantity of pollen is rarely a limiting factor in maize production.

Ear shoots. Ear shoots are initiated 6-8 nodes below the tassel and at lower nodes. Although buds occur at numerous nodes, only 1-3 ear shoots eventually form ears.

Initiation of axillary buds begins at the base of the stem and proceeds upwards. However, differentiation of buds into ear shoots proceeds from the uppermost bud towards the base of the plant.

Ear shoot initiation occurs about 10 days after tassel initiation. Ear elongation stops first at lower nodes giving top ears more time to develop and accumulate assimilates.

The internodes on lateral branches bearing the female inflorescence are shortened, so that the husk leaves overlap and cover the developing ear (Figure 12). Female spikelets are in pairs, therefore maize ears always have an even number of rows. Each spikelet contains one fertile ovule. A typical maize ear has 500-750 ovules or potential kernels.

Each ovule produces a silk (style) which is stigmatic (receptive for pollen germination) for most of its length. The maize style is longer than that of any other species in the plant kingdom. The first silks to emerge from the husk are those from the base of the ear. Appearance of silk on the ear marks the growth stage R1.

Because maize is protandrous (male flowers mature before female flowers), silks receive pollen as soon as they emerge. The period between pollen shed (anthesis) and silk emergence (stage R1) is called anthesis-silking interval. This interval is a measure of protandry, and is related to tolerance to stresses which reduce photosynthesis at flowering.

Under Favorable conditions, silks emerge 1-3 days after anthesis and remain fertile for about 1 week before senescing at thier base. Harsh weather can cause silks to dry up or delay silk emergence. Poor 'nicking' (lack of synchrony of anthesis and silk emergence) is largely a result of delayed silk emergence.

Under certain conditions, when growth is vigorous and unstressed, female flowers mature before male flowers (protogyny). Fertilization and yield may not be adversely affected if anthesis occurs up to 5 days after silk emergence.

Moist, sticky hairs for catching pollen cover the silks. Pollen grains germinate within a few minutes after reaching the silks. The pollen tubes grow down the silks in 12-28 hours to fertilize the ovules.