Kids Research Express

Sexual Propagation

In nature, sexual propagation begins when water, wind, insects, birds, or small mammals carry pollen randomly between plants (see Pollination). In flowering plants, this transfer of pollen enables the male sex cells, or sperm, of one flower to fertilize the female sex cell, or egg, of a second flower (see Fertilization).

The egg is located at the base of the flower in a structure called an ovule, found within the ovary. Depending on the species, an ovary contains one, several, or many ovules. The ovaries of peach and avocado flowers, for example, have one ovule, while those of watermelon and cantaloupe have many.

As the fertilized egg (or eggs) within the ovule begins to develop into an embryonic plant, it produces a variety of hormones that stimulate the outer wall of the ovule to harden into a seed coat. Other biochemical changes in the ovule produce a starchy substance that will be used as a food supply. In this way, the ovule ripens into a seed—a structure containing an embryonic plant and its food supply surrounded by a seed coat. The ovary, which houses the ovule or ovules, is also stimulated by hormones, which cause its tissues to enlarge into a fruit. The fruit contains the ripened ovules, or seeds.

Plant Propagation

Plant Propagation, growing new plants from seeds or from parts of existing plants. Plant propagation occurs in nature to ensure survival and spread of species. It is also used commercially to produce seeds and plants for agriculture, horticulture, and forestry. Plant propagation includes sexual propagation, which involves the union of sperm and egg to form seeds, and asexual propagation. Asexual propagation, also known as vegetative propagation, is the growing of new plants from a leaf, stem, or root of a single parent plant (see Vegetative Reproduction). These two forms of plant propagation transmit genetic information between plants of the same species. Genetic engineering transfers genes from one organism to another that may or may not be of the same species to introduce desirable traits into an organism. These so-called transgenic plants can then be propagated by sexual propagation or asexual propagation.

Ecology

Ecology, the study of the relationship of plants and animals to their physical and biological environment. The physical environment includes light and heat or solar radiation, moisture, wind, oxygen, carbon dioxide, nutrients in soil, water, and atmosphere. The biological environment includes organisms of the same kind as well as other plants and animals.

Because of the diverse approaches required to study organisms in their environment, ecology draws upon such fields as climatology, hydrology, oceanography, physics, chemistry, geology, and soil analysis. To study the relationships between organisms, ecology also involves such disparate sciences as animal behavior, taxonomy, physiology, and mathematics.

An increased public awareness of environmental problems has made ecology a common but often misused word. It is confused with environmental programs and environmental science (see Environment). Although the field is a distinct scientific discipline, ecology does indeed contribute to the study and understanding of environmental problems.

The term ecology was introduced by the German biologist Ernst Heinrich Haeckel in 1866; it is derived from the Greek oikos (“household”), sharing the same root word as economics. Thus, the term implies the study of the economy of nature. Modern ecology, in part, began with Charles Darwin. In developing his theory of evolution, Darwin stressed the adaptation of organisms to their environment through natural selection. Also making important contributions were plant geographers, such as Alexander von Humboldt, who were deeply interested in the “how” and “why” of vegetational distribution around the world.

Horticulture

Horticulture (Latin hortus,”garden”; cultura,”cultivation”), science and art of growing fruits, vegetables, flowers, shrubs, and trees. Horticulture originally meant the practice of gardening and, by extension, now means the cultivation of plants once grown in gardens. In contrast, the term agriculture, by derivation, referred to more open forms of culture such as the production of grains and grasses, known as agronomic crops, which are cultivated on a large scale. The original distinctions have been so blurred that many crops formerly considered either agronomic or horticultural are now categorized sometimes in one field, sometimes in the other, depending on the intended use of the crop. Thus a plant grown for home consumption may be called horticultural; the same plant cultivated for forage is regarded as an agronomic crop.

Horticulture includes the growing of fruit (especially tree fruits), known as pomology; production of vegetable crops, called olericulture; production of flowers, termed floriculture; and ornamental horticulture, known also as landscape gardening, which includes the maintenance and design of home grounds, public gardens and parks, private estates, botanical gardens, and recreational areas such as golf courses, football fields, and baseball diamonds.

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Floriculture

Floriculture, cultivation of ornamental flowering plants for aesthetic purposes, whether grown in window boxes, greenhouses, or gardens. In floriculture, plants are grown for individual effect; in landscape gardening, for total effect. Although flowers have been cultivated since the rise of civilizations, commercial cultivation in greenhouses of plants and flowers native to other countries was not established until the 19th century. See also Horticulture.