rating) Some plants have flowers that are not perfect, they do not have both male and female reproductive parts in the same structure. Instead they produce male flowers that have only stamens or female flowers that have only pistils. Monecious plants have both male and female flowers rather that perfect flowers.

Corn (maize) is a good example of a monecious plant species. It has two types of flowers that develop at different parts of the plant. The male flower forms at the top of the plant and is called the tassle. Because of the way grasses such as corn grows, the tassle starts to develop inside the plant and then emerges just a day or so before it is mature and ready to produce and shed pollen. A tassle actually consists of hundreds of male flowers that have stamens but no pistils.


Tassle and maize plant.
Image by UNL
Purple Tassle on the left has anters emerged,
green tassle does not.
Image by Joel Stuthman

The monecious corn plant has female flowers that develop on the side of the plant and emerge from the leaf node. As these flowers emerge they are called the shoot and they develop into the familiar ear of corn. These flowers only have pistils. The styles of corn are long and grow up from the ovary and out of the sepals (husks). They are called silks because of their length and delicate nature. When pollen from the tassle flower lands on the stigma at the end of the silk, the pollen tube can grow through the silk to the ovary. Obviously corn pollen is capable of growing a long tube!


Ear or shoot flower
on corn plant.
Image by UNL
Silks being pollinated.
Image by Joel Stuthman


Long silks connect

Female flowers are borne on the ear. The female sexual organ in flowers is called the pistil, and the pistil is composed of an ovary, a style, and a stigma (Figure 1). For corn, the ovary will mature to become the kernel, and the ovary wall becomes the outer “skin” of the kernel. Like all grass plants the corn ovary contains only one ovule (a seed is a mature ovule), so when the kernel matures there will be one seed inside each kernel. And, the seed coat fuses tightly to the ovary wall so they cannot be easily separated. The style is highly elongated and called the silk. The stigma is found at the end of the silk and is about one half inch long. The stigma looks like the rest of the silk except that it usually possesses more hairs (trichomes). Although these are technical terms, each of these parts play a role in successful corn fertilization.

Ear development begins early in the life cycle of the corn plant. Ear shoots are microscopic at first and located at stem nodes. Ear shoot growth occurs hidden within the leaf sheaths. If you remove all corn leaves including the sheaths as many as 8 to 10 ear shoots are large enough to be seen without a magnification. Most modern corn hybrids produce a single large ear because the topmost ear shoot dominates all of the other ear shoots.

Between growth stages V5 (5 leaf collars visible) and R1 (silking), primary ear shoot development coincides with tassel development and rapid stem elongation. First, the number of rows of flowers is determined. This number will always be even (e.g. 14, 16, 18) unless a mutation or some odd weather condition had occurred. Second, the number of flowers in each row is determined. Flowers are added to the tip of the ear in response to conditions the plant perceives at this time. Good nitrogen nutrition, high light levels (few weeds), and plentiful sugar production from photosynthesis (good weather) all lead to more flowers per row, and thus, larger ear size.

A corn ear several days after growth stage R1.Figure 2. A corn ear several days after growth stage R1. All husks have been removed.

Silks begin to elongate at about growth stage V12. Silks from flowers near the butt of the ear (closest to the stem) begin to elongate first. Silk from flowers near the tip of the ear begin elongation last. Silk elongation rates also differ among flower positions on the ear, so that silks from flowers near the butt emerge from husks several days before silks from the ear tip. Remember that there is one silk for each flower, so as many as 1000 silks push their way along the ear and within the husks (Figure 2).

The driving force for silk elongation is water pressure. The female flower absorbs water from the cob and the resulting pressure pushes the tip of the silk (stigma) forward. With 1000 silks all elongating at same time the “traffic” often is hectic. The time sequence of silk elongation – from base to tip –, the nearly straight rows of flowers, and small channels on the inside of the husks all give order to the elongation process. And, it works almost flawlessly most of the time. Sometimes silk traffic jams occur and the silks tangle leading to a condition called “silk balling”. When this occurs, some to most of the silks on the ear will not be able to position themselves so that they intercept pollen. Fortunately, this occurrence is rare.

Intact corn ear at growth stage R1