Botany: Historical Development

Botany: Historical Development

Because civilization rests in part on a knowledge of plants and their cultivation, botany can be said to have originated with the first cultivation of crops, which may date from 9000-7000 bc. Not until about 2300 years ago, however, did humans become interested in plants for their own sake. Thus, botany as a pure science began in the 4th century BC with the Greek philosopher Theophrastus, whose treatises on the classification, morphology, and reproduction of plants heavily influenced the discipline until the 17th century. Indeed, modern botany began to develop only about the 16th century, at least in part because of the invention of the microscope (1590) and of printing with movable type (1440).

The Greeks believed that plants derived their nourishment from the soil only. Not until the 17th century did the Belgian scientist Jan Baptista van Helmont show that, although only water was added to a potted willow, it gained nearly 75 kg (165 lb), whereas the soil it stood in lost only about 60 g (about 2 oz) of weight over a period of five years. This demonstrated that the soil contributes very little to the increase in the weight of plants. In the 18th century the English chemist Joseph Priestley demonstrated that growing plants “restore” air from which the oxygen has been removed (by the burning of candles or the breathing of animals), and the Dutch physiologist Jan Ingenhousz (1730-99) extended this observation by showing that light is required for plants to restore air. These and other discoveries formed the basis for modern plant physiology, that branch of botany dealing with basic plant functions.

That water moves upward through the wood and that solutes move downward through the stems of plants was discovered independently in the 17th century by Marcello Malpighi in Italy and Nehemiah Grew in England. These facts have now been known for some 300 years, but only in the last few years have acceptable theories explaining the movements of liquids in plants been developed, using a variety of refined analytical techniques.

Botany

Botany

Botany, branch of biology concerned with the study of plants (kingdom Plantae). Plants are now defined as multicellular organisms that carry out photosynthesis. Organisms that had previously been called plants, however, such as bacteria, algae, and fungi, continue to be the province of botany, because of their historical connection with the discipline and their many similarities to true plants, and because of the practicality of not fragmenting the study of organisms into too many separate fields.

Botany is concerned with all aspects of the study of plants, from the smallest and simplest forms to the largest and most complex, from the study of all aspects of an individual plant to the complex interactions of all the different members of a complicated botanical community of plants with their environment and with animals (see Ecology).

See also Historcal Development; Classical Studies.

related articles:

• plant breeding
• botanical garden
• diseases of plants
• floriculture, growing of flowering plants
• horticulture, growing of cultivated plants

Controlling Garden Pests

Controlling Garden Pests
Three types of pests can plague gardens: weeds, insects, and diseases. A weed is any plant that grows where the gardener does not want it. Weeds are undesirable because they compete with garden plants for light, water, and nutrients. Common methods for controlling weeds include pulling them up by hand; digging them out; and cutting them off using a hoe or mower. One way to slow the growth of weeds is to cover the soil with a layer of mulch, which blocks out the light and air that weeds need to grow. Weeds also can be controlled by treating them with a weed killer, or herbicide. Like fertilizers, weed killers can be organic or synthetic (see See also Weed Control).

Insects damage plants by chewing leaves or other plant parts by sucking the liquid from the plant, or in some cases, by transmitting viruses. Another method for preventing insect damage is to cover young plants with a floating row cover, which is a very thin, white, gauzy blanket that keeps many insects away from the plants. Another preventive method is to grow plants bred for resistance to insect pests.

Some insects can be kept in check by introducing beneficial bacteria or insects to the garden. This method exploits the natural ecological relationships between garden pests and other organisms. Ladybugs, for instance, eat aphids, one of the more notorious garden insect pests, and certain types of bacteria kill insect larva. Another method to help control insects in vegetable and flower gardens is to rotate crops instead of growing the same type of plant in the same place every year. Many insects have a life cycle that depends on the presence of a certain type of plant. By removing the plant for at least two years, the life cycle can be interrupted, thus controlling the pest. Both organic and synthetic insect-killing materials, called insecticides, also are available to control insect pests (see Pest Control).

Diseases caused by fungi, bacteria, or viruses also can damage plants (see Diseases of Plants). In most cases, once a plant has a disease it cannot be saved, though some fungal diseases can be controlled with a fungicide. The best approach to disease prevention is to provide plants with optimum soil, nutrients, light, and water so they can fight off disease, and to grow plants that have been bred for disease resistance or have natural resistance.

Harvesting and Pruning

Gardeners harvest plants at different stages, depending on how the harvested plants or plant parts are used. Crops grown for their fruit, such as tomatoes and eggplant, are harvested when the fruit is ripe. Some plants are harvested before they flower—lettuce and spinach, for example, are grown for their tender leaves and develop a bitter flavor if allowed to flower. Plants grown for their roots, such as carrots and radishes, are harvested when the root is large enough, but before it gets tough or woody and loses its sweetness. In flower gardens, the sign of maturity is the formation of seeds. Many plants stop flowering once they set seed, so to make plants produce flowers longer, gardeners can remove the faded flowers before they produce seed, a technique called deadheading.

Gardeners may attempt to control the shape of woody plants, such as trees and shrubs, by removing, or pruning, branches growing in the wrong direction. They also prune to removed damaged, disease, or dead branches. Some shrubs, such as lilacs, bear the most flowers in young wood, so gardeners remove the oldest branches. Gardeners prune plants at different times of the year, depending on how they hope to affect the plant’s growth.

Soil Management

Soil Management

Soil Management, the basis of all scientific agriculture, which involves six essential practices: proper tillage; maintenance of a proper supply of organic matter in the soil; maintenance of a proper nutrient supply; control of soil pollution; maintenance of the correct soil acidity; and control of erosion.

TILLAGE

The purpose of tillage is to prepare the soil for growing crops. This preparation is traditionally accomplished by using a plow that cuts into the ground and turns over the soil. This removes or kills any weeds growing in the area, loosens and breaks up the surface layers of the soil, and provides a bed of soil that holds sufficient moisture to permit the planted seeds to germinate. Traditional tillage may harm the soil if used continuously over many years, especially if the fertile topsoil layer is thin.

MAINTENANCE OF ORGANIC MATTER

Organic matter is important in maintaining good physical conditions in the soil. It contains the entire soil reserve of nitrogen and significant amounts of other nutrients, such as phosphorus and sulfur. Soil productivity thus is affected markedly by the organic-matter balance maintained in the soil. Because most of the cultivated vegetation is harvested instead of being left to decay, organic materials that would ordinarily enter the soil upon plant decomposition are lost. To compensate for this loss, various standardized methods are employed. The two most important of these methods are crop rotation and artificial fertilization.

NUTRIENT SUPPLY

Among soil deficiencies that affect productivity, deficiency of nutrients is especially important. The nutrients most necessary for proper plant growth are nitrogen, potassium, phosphorus, iron, calcium, sulfur, and magnesium, all of which usually exist in most soils in varying quantities. In addition, most plants require minute amounts of substances known as trace elements, which are present in the soil in very small quantities and include manganese, zinc, copper, and boron. Nutrients often occur in the soil in compounds that cannot be readily utilized by plants.

SOIL POLLUTION

Soil pollution is the buildup in soils of persistent toxic compounds, chemicals, salts, radioactive materials, or disease-causing agents, which have adverse effects on plant growth and animal health. As of now, soil pollution is not widespread. Although the application of fertilizers containing the primary nutrients, nitrogen, phosphorus, and potassium, has not led to soil pollution, the application of trace elements has. The irrigation of arid lands often leads to pollution with salts. Sulfur from industrial wastes has polluted soils in the past, as has the accumulation of arsenic compounds in soils following years of spraying crops with lead arsenate. The application of pesticides has also led to short-term soil pollution. See Environment.