The plant flowers and sets fruit

Flowering—the formation of reproductive organs—may be initiated when the plant reaches an appropriate age or size. Some plant species, however, flower at particular times of the year, meaning that the plant must be capable of distinguishing different times of the year. In these plants, the leaves measure the length of the night (shorter in summer, longer in winter) with great precision. Light absorption by photore-ceptors is the first step in this time-measuring process.

Once the leaves have determined that it is time for the plant to flower, that information must be transmitted as a signal to the places where flowers will form. The means by which this signal is transmitted remains a mystery, but it is likely that a "flowering hormone" travels from the leaf to the point of flower formation.

After flowers form, hormones play further roles in reproduction. Hormones and other substances control the growth of the pollen tube that brings sperm and egg together. Following fertilization, a fruit develops and ripens under hormonal control.

38.1 Patterns of Early Shoot Development (a) In grasses and some other monocots, growing shoots are protected by a coleoptile until they reach the soil surface. (b) In most eudicots, the growing point of the shoot is protected by the cotyledons, (c) In some other eudicots, the cotyledons remain in the soil, and the growing point is protected by the first true leaves.

lj A coleoptile (a cylindrical sheath of cells) protects the early shoot as it grows to the soil surface.

(b) Eudicots (bean) 1Ï The shoot apex of most eudicots

lj A coleoptile (a cylindrical sheath of cells) protects the early shoot as it grows to the soil surface.

(b) Eudicots (bean) 1Ï The shoot apex of most eudicots

Shoot Apex Eudicot

The cotyledons of peas remain in the soil.

2) After the shoot emerges from the soil, it continues to elongate and the leaves emerge.

Primary root

2) After the shoot emerges from the soil, it continues to elongate and the leaves emerge.

The cotyledons of peas remain in the soil.

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Essentials of Human Physiology

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