Bacteria

Bacteria, one-celled organisms visible only through a microscope. Bacteria live all around us and within us. The air is filled with bacteria, and they have even entered outer space in spacecraft. Bacteria live in the deepest parts of the ocean and deep within Earth. They are in the soil, in our food, and on plants and animals. Even our bodies are home to many different kinds of bacteria. Our lives are closely intertwined with theirs, and the health of our planet depends very much on their activities.

Bacterial cells are so small that scientists measure them in units called micrometers (µm). One micrometer equals a millionth of a meter (0.0000001 m or about 0.000039 in), and an average bacterium is about one micrometer long. Hundreds of thousands of bacteria would fit on a rounded dot made by a pencil.

Bacteria lack a true nucleus, a feature that distinguishes them from plant and animal cells. In plants and animals the saclike nucleus carries genetic material in the form of deoxyribonucleic acid (DNA). Bacteria also have DNA but it floats within the cell, usually in a loop or coil. A tough but resilient protective shell surrounds the bacterial cell.

Biologists classify all life forms as either prokaryotes or eukaryotes. Prokaryotes are simple, single-celled organisms like bacteria. They lack a defined nucleus of the sort found in plant and animal cells. More complex organisms, including all plants and animals, whose cells have a nucleus, belong to the group called eukaryotes. The word prokaryote comes from Greek words meaning “before nucleus”; eukaryote comes from Greek words for “true nucleus.”

Diseases of Plants

Diseases of Plants

Diseases of Plants, deviations from the normal growth and development of plants incited by microorganisms, parasitic flowering plants, nematodes, viruses, or adverse environmental conditions. In the United States alone, known plant diseases attributable to these causes are estimated to number more than 25,000; the estimated annual losses therefrom add up to several billion dollars. Injuries to plant life due primarily to insects, mites, or animals other than nematodes are not regarded as plant diseases.

BACTERIA-INDUCED DISEASES -> Bacterial diseases are marked by various symptoms, including soft rot, leaf spot, wilt of leaves and stems, canker, leaf and twig blight, and gall formation. Fire blight, a disease of apple and pear trees, is historically interesting because it was the first plant disease in which a bacterium was shown to be the inciting agent. Infected trees exhibit a blackening of the flowers, leaves, and twigs, and the disease finally may involve the entire tree, causing serious damage and even death. Citrus canker, an Asian disease of the orange tree and its relatives, is characterized by corky growths on the fruit, leaves, and twigs. See also Bacteria.

DESTRUCTIVE FUNGI -> The majority of plant diseases are incited by fungi. Fungus diseases have been observed and commented on since ancient times. Equally large numbers of fungi in other groups produce a large array of diseases characterized by leaf spots, ulcerous lesions, blights, powdery and downy mildews, cankers, wood rots and stains, root rots, wilts, club root, and various other symptoms.

VIRAL INFECTIONS -> Typical symptoms of viral infections include mosaic patterns, yellowing of foliage, veinclearing, ring spots, stunting and premature death, malformations, and overgrowth. Under some conditions the symptoms may be masked. See also Virus.

NEMATODES -> Nematodes, or roundworms, are an important cause of disease in plants. For many years attention was focused on the root-knot nematodes, which cause fleshy root knots or galls on plants. More recent investigations were concerned with other species, including the stem or bulb nematodes, which live in the leaves, stems, bulbs, and roots of narcissus, phlox, and many other plants, and the leaf nematodes, growing in herbaceous plants including the begonia and chrysanthemum.

Botanical Garden

Botanical Garden
Botanical Garden, garden in which plants are grown and displayed primarily for scientific and educational purposes. A botanical garden consists chiefly of a collection of living plants, grown out-of-doors or under glass in greenhouses and conservatories. It usually includes, in addition, a collection of dried plants, or herbarium, and such facilities as lecture rooms, laboratories, libraries, museums, and experimental or research plantings.

The plants may be arranged according to one or more subdivisions of botanical science. The arrangements may be systematic (by plant classification), ecological (by relation to environment), or geographic (by region of origin). The larger botanical gardens often include special groupings, such as rock gardens, water gardens, wildflower gardens, and collections of horticultural groups produced by plant breeding, such as roses, tulips, or rhododendrons. A plantation restricted to exhibits of woody plants is called an arboretum.

related articles:

• floriculture
• gardening
• horticulture
• plant breeding

Plant Breeding

Plant Breeding
Plant Breeding, the practical application of genetic principles to the development of improved strains of agricultural and horticultural crops. Plant breeders can adapt old crops to new areas and uses; increase yields; improve resistance to disease; enhance the nutritional quality and flavor of fruits and vegetables; and develop traits that are useful for storage, shipping, and processing of foods. Improved wheat and rice varieties sparked the green revolution in the developing world during the 1960s and '70s. In ornamental plants, breeders have developed larger and showier flowers, greater plant vigor, and myriad types, shapes, and colors.

For more information about Plant Breeding, read the full article at wikipedia.org.

Botany Classical Studies

Botany Classical Studies

Gross observations and experiments on photosynthesis and the movement of water in plants can be made without knowledge of their structure, but explanations of these phenomena require knowledge of morphology—the study and interpretation of plant form, development, and life histories—and of anatomy—the study of plant tissues and their origin and relations to one another. The cellular nature of plants was first pointed out by the English scientist Robert Hooke in the 17th century, when he observed that cork bark consists of cells. In 1838 the German botanist Matthias Schleiden proposed that all plant tissues consist of cells; this implied a basic sameness of living things and laid the foundation for the development of cytology, the study of the structure and function of cells as individual units rather than as aggegrate tissue. The German pathologist Rudolf Virchow showed in 1858 that cells are derived from preexisting cells, and thus that a continuity exists between past and present living things.

Such observations were important not only in the development of plant physiology and anatomy but also in the understanding of genetics, the science of heredity, and of evolution.

Knowledge of anatomy, genetics, and evolution has greatly advanced plant classification by providing a rational basis for this subdivision of botany. The 17th-century British naturalist John Ray divided plants into nonflowering and flowering types, and flowering plants into dicots and monocots. The 18th-century Swedish botanist Carolus Linnaeus, however, provided the framework on which modern classifications are based and, just as important, a simplified system of nomenclature in which each plant is given two names: the first the name of the genus and the second the name of the species.