Plant Morphology The expression Morphology is derived from

Plant Morphology The expression “Morphology” is derived from two Latin words (Morphe = form + logos = study). It deals with the study of forms and features of different plant organs like roots, stems, leaves, flowers, seeds, fruits, …. etc.

The body of a typical plant is differentiated into: An underground root system An aerial shoot system. The shoot system consists of stem (including branches), leaves, flowers and fruits. The roots, stems and leaves are vegetative parts, while flowers constitute the reproductive part.

Adaptation: Any alteration in the structure or function of an organism or any of its part that results from natural selection and by which the organism becomes better fitted to survive and multiply in its environment.

SEEDS A seed (mature ovule) is a miniature plant with a protective cover in a suspended state of development. Most seeds contain a built-in food supply called endosperm. The endosperm can be made up of proteins, carbohydrates, or fats.

Function 1. Propagation 2. Feed 3. Horticultural uses 4. Food 5. Oil

The three primary parts of a seed are: 1. The embryo, is the young multicellular organism before it emerges from the seed. 2. Endosperm, is a source of stored food, consisting primarily of starches. 3. Seed coat, consists of one or more protective layers that encase the seed.

A seed begins to form an embryo following fertilization and the start of a zygote. The mature embryo consists of an embryonic root known as the radicle, an embryonic shoot known as the plumule, and one or two cotyledons. The plumule has two main parts, the epicotyl and the hypocotyl. The epicotyl is the portion of the embryonic stem above the point at which the stem is attached to the cotyledon(s). The hypocotyl is the portion below the point of attachment which connected to the radicle.

The cotyledon is described as a seed leaf that stores food in the form of starch and protein for use by the embryo. The seed is encased in a protective seed coat. It protects the embryo and the endosperm from drying and from physical injury. A scar can be seen at the end or along the side of the seed coat. It is called the hilum. The hilum marks the point of attachment of the seed to the ovary wall. The seed coat has a tiny opening, sometimes visible near the hilum, called the micropyle.

SEED GERMINATION • Germination is defined as the emergence and development from the seed embryo of those essential structures which indicates its ability to produce a normal plant under favorable conditions. • Seed germination depends on both internal and external conditions. • The most important external factors include right temperature, water, oxygen or air and sometimes light or darkness.

Water Mature seeds are often extremely dry and need to take in significant amounts of water. The uptake of water by seeds is called imbibition, which leads to the swelling and the breaking of the seed coat. When seeds are formed, most plants store a food reserve with the seed, such as starch, proteins or oils. This food reserve provides nourishment to the growing embryo. When seed imbibes water, hydrolytic enzymes are activated which break down these stored food resources into metabolically useful chemicals.

After the seedling emerges from the seed coat and starts growing roots and leaves, the seedling's food reserves are typically exhausted; at this point photosynthesis provides the energy needed for continued growth and the seedling now requires a continuous supply of water, nutrients, and light.

Oxygen is used in aerobic respiration, the main source of the seedling's energy until it grows leaves. If a seed is buried too deeply within the soil or the soil is waterlogged, the seed can be oxygen starved. Some seeds have impermeable seed coats that prevent oxygen from entering the seed, causing a type of physical dormancy which is broken when the seed coat is worn away enough to allow gas exchange and water uptake from the environment.

Temperature affects cellular metabolic and growth rates. Seeds often have a temperature range within which they will germinate, and they will not do so above or below this range. Many seeds germinate at temperatures slightly above 16 -24 C, while others germinate just above freezing and others germinate only in response to alternations in temperature between warm and cool. Some seeds germinate when the soil is cool (-2 - 4 C), and some when the soil is warm (24 -32 C). Some seeds require exposure to cold temperatures to break dormancy.

Light or darkness. Most seeds are not affected by light or darkness, but many seeds, including species found in forest settings, will not germinate until an opening in the canopy allows sufficient light for growth of the seedling

Types of Germination

Epigeal Germination: • Characteristic of bean and pine seeds and is considered evolutionarily more primitive than hypogeal germination. • During germination, the cotyledons are raised above the ground where they continue to provide nutritive support to the growing points.

• During root establishment, the hypocotyls begin to elongate in an arch that breaks through the soil, pulling the cotyledon and the enclosed plumule though the ground and projecting them into the air. • Afterwards, the cotyledons open, plumule growth continues and the cotyledons wither and fall to the ground.

Hypogeal Germination: • Characteristic of pea seeds, all grasses such as corn, and many other species. • During germination, the cotyledons remain beneath the soil while the plumule pushes upward and emerges above the ground. • The epicotyl is the rapidly elongating structure. • Regardless of their above-ground or below-ground locations, the cotyledons continue to provide nutritive support to the growing points throughout germination.

Seed Growth and Development Terms Dormancy State of suspended growth to survive adverse conditions and aid in dispersion Seed coat dormancy When the seed coat is impermeable to water and gases (oxygen). It requires action by weathering, microorganisms, passage through an animal's digestive track, or fire to soften the seed coat.

Embryo dormancy This is due to physiological conditions or germination blocks in the embryo itself. It requires a specific period of cold (or heat) with available moisture and oxygen. Embryo dormancy is common in woody plants.

Double dormancy Condition of both seed coat and embryo dormancy Rudimentary embryo dormancy Situation where the embryo is immature and requires a growth period before it can germinate Chemical inhibitor dormancy Seed contains some type of chemical that blocks germination. Many desert plants contain chemical germination inhibitors that are leached out in a soaking rain.