Skip to main content

Biology: Botany

Biology: Botany

Introduction

Botany is the scientific study of plants. Both as an independent science and as a companion to other scientific disciplines, the contributions of botanists and botany have proved pivotal to many fundamental advances in science. Modern genetics was, for example, built upon a foundation of experimentation with plants.

Botany is much more than the study of plant anatomy and classification schemes; it is a vibrant quest to understand plant life and processes and to ask and answer important theoretical and practical questions that are key to understanding and preserving all life.

Historical Background and Scientific Foundations

Classification Systems

Humans have used plants as medicine since the beginning of civilization. Possibly as early as the Neanderthal man, plants were used for therapeutic purposes. The earliest recorded attempts of phytotherapy (medicinal use of plants and their extracts) are found in Babylon starting in about 1770 BC in the Code of Hammurabi and in ancient Egypt around 1550 BC. Indeed, ancient Egyptians believed medicinal plants would be useful even in the afterlife of their pharaohs.

Attempts to classify plant life also date back to civilization's earliest origins. Archaeologists have recovered records and artifacts that reveal varied systems of classification in different cultures. By the rise of ancient Egyptian, Greek, Roman, and Chinese civilizations, varied classification systems supported the practical trade and use of plants, especially those used in agriculture, medicine, or various religious rites.

The Greek philosopher Aristotle (384–322 BC) advanced a classification system that served to separately group both plant and animal life. Plant classification was principally based upon common observable morphological characteristics (e.g., size and shape).

Roman Pliny the Elder's (c.AD 50) Natural History contained substantial writings devoted to botanical science, especially plants used in agriculture and medicine. Along with Greek philosopher Dioscorides' (c.AD 40–90) Materia Medica these texts were the fundamental botanical reference works in use for more than a millennium.

Over the course of the next thousand years most European physicians based their medical care mainly upon the teachings of Galen of Pergamum (c.131–c.201), who was born in what is now Bergama, Turkey. Galen's writings were prolific, and were based upon his belief that the body had four humors, or bodily fluids (blood, phlegm, yellow bile, and black bile), which were related to the four elements of external nature (earth, air, fire, and water). Galen taught that illness stems from an imbalance of the humors and the elements, and that restoring this balance would affect a cure. Galen described over 300 pharmaceutical remedies (mostly herbal concoctions).

Studies of plants into the Western Medieval era remained linked to mystical and religious practice. Descriptions of plants rested upon a “doctrine of signatures” in which the supposed divine plan of the use of a plant was to be determined by careful study of a plant's shape, color, etc.

By the year 700, during what is referred to as the Dark Ages in Europe, monasteries became the refuge for those with illnesses not amenable to home style herbal remedies or rituals. The role of women in medieval healthcare actually expanded as fewer trained physicians were available. Many women possessed a rudimentary knowledge of herbal remedies, and those with greater knowledge or skill became village healers. A few women wrote medical texts. Hildegard of Bingen (1098–1179), a German Benedictine herbalist, practiced medicine in her role as abbess of Rupertsberg. Hildegard's Book of Simple Medicine was a compendium of traditional lore featuring herbalism, religion, superstition, and folk medicine. Hildegard wrote on the natural causes of disease, advising treatment on the principle of opposites. Hildegard claimed that herbs were a gift from God, and those unable to be healed by herbs were willed by God to die.

Approximately 300 years later, as men regained the prominent role in healthcare delivery, women healers were ostracized from professional medical organization and, on occasion, were executed as witches for use of herbal remedies and potions.

In early eighth century England, monks in then-remote North Umberland produced a medical book in the non-Latin language of Anglo-Saxon. The monks—among them, the Venerable Bede (c.673–735)—referred to the English healer as laece, or leech, and cited extensive plant remedies. Later, the Lorch Book of Medicine, written about 795 in a German Benedictine abbey, discusses the humors, and contains a brief text on simple anatomy and prognostics. The book also contained therapeutic recipes, dietary treatments, and other practical advice for tending the sick.

In approximately 950, England's King Alfred was convinced by a British nobleman to commission a manual of the established medical treatments of the day. The Leech Book of Bald combined the herbal practices of the Celts and Anglo-Saxons with that of the GrecoRomans and Arabs. Compiled by Bald, and scribed by a monk named Clid, the Leech Book of Bald is the oldest surviving Anglo-Saxon medical text. The book contains simplified Latin recipes with local ingredients replacing the exotic ones found in Mediterranean or Arab lands. Some scholars assert that the simplified language implies the book was intended to be shared with any of the literate population and was meant to serve as a layman's manual, as well as the trained healer's aid. The book contains extensive herbal remedies containing mugwort, periwinkle, violets, vervain, wood betony, and yarrow, among other botanical treatments.

In the thirteenth century, German naturalist Albertus Magnus (c.1200–1280) made extensive studies of plants in support of his arguments for the creation of life via “spontaneous generation.” The advent of the Renaissance saw horticultural practices broadened from the convent and monastery into uses of flowers and plants in art and landscape architecture (e.g., pubic parks in regions of Padua, Pisa, and areas of what is now Tuscany). The Age of Exploration and the return of plants from exotic lands continually presented new species for study.

A resurgence in botanical study resulted both from the increased appreciation of plants and the establishment of large scale depositories for the production of medicinal herbs for Societies of Apothecaries that were becoming influential throughout Europe. Books on herbal medicine were published, and much of this work traced its origins to pharmacopoeias written by German physician and botanist Valerius Cordus (1515–1544).

The New World was also a site of intense botanical interest. In 1672, English botanist John Josselyn (fl. 1638–1675) lists 23 plants brought to England from America; by 1713 there were at least 400 such new plants in England. In 1675, Josselyn published an account of the plants and animals he encountered while living in America.

Plants were a life-long fascination with Carl Linnaeus (1707–1778; also known as Carolus Linnaeus or Carl Linné). While undertaking studies in medicine, Linnaeus was continually found working in his university's botanical gardens with collections of rare tropical and foreign plants. His keen observation of plant sexuality was evident as early as 1735 in his books System Naturae and his subsequent Genera Planetarum (published in 1737).

The most elegant classification scheme resulted from the work of Linnaeus and his 1753 publication of Species Planetarium, which established the paradigms (the standardized protocols) upon which modern classification and nomenclature (the principles used to name species) are based.

Linnaeus's system combined observations of phenotypical expression (observable characteristics) with a hierarchical (multi-level) system that grouped plants according to their similarities. Place in the hierarchy depended on the number of shared characteristics among specimens.

Linnaeus' work built upon that of Swiss botanist Gaspard Bauhin's (1560–1624) Pinax theatri botanici (Illustrated exposition of plants; published 1596), the work of German Botanist Joachim Jung (1587–1657), and the work French botanist Joseph Pitton de Tourne-fort (1656–1708) who in 1694 published Eléments debotanique, ou Méthode pour reconnaître les Plantes, which was the work that made clear distinctions between genus and species. Linnaeus also extended the work of French Botantist Pierre Magnol's (1638–1715) Prodromus Historiae Generalis Plantarum, which was one of the first attempts to form a rational classification of plants into families.

IN CONTEXT: CLASSIFICATION AS DIVINE CALLING

The desire of Carl Linnaeus (1707–1778; also known as Carolus Linnaeus or Carl Linné) to classify all living things often bordered on the compulsive; he believed his work to be divinely inspired and considered those who did not follow his system to be “heretics.” However, he was also a skilled and caring instructor who nurtured the interests of his many students, often sending them abroad to the Middle East, China, and the Pacific Islands for new specimens. In 1761, Linnaeus was given the noble title von Linné, and although the King of Spain offered him generous compensation to settle in his country, Linnaeus remained in Sweden until his death after a stroke in 1778.

In the modern era, for example, the Kingdom Plantae (Plants) is composed of species that share essential characteristics, i.e. they are multicellular and eukaryotic (they have a defined cell nucleus enclosed in a membrane, have a cellulose cell wall, are nonmotile, are auto-trophic via photosynthesis, etc.).

Prior to Linnaeus most species were identified by polynomial names (usually long descriptive Latin phrases), but Linnaeus advanced use of a binomial nomenclature that created a simplified unique Latin name from the genus and species name. For example Quercus alba is the scientific name for white oaks, while Quercus rubra is the scientific name for red oaks. Both white and red oaks share the characteristics of the oak genus Quercus, while each unique species is given a specific epithet, e.g. alba (white) or rubra (red).

Contributions from the Americas continued to spur European interest. French botantist André Michaux (1746–1802) published the first book of American flora or plants that is national in scope. His Flora Boreali-Americana was published posthumously in Paris and has many plates drawn by French artist Pierre-Joseph Redouté (1759–1840).

In addition to contributing to European based science, America began to develop its own culture of observation and investigation. In 1836, American botanist Asa Gray (1810–1888) published his Elements of, Botany, argued to be the first botany text published in the United States.

Botany and Botanists Facilitate Great Advances in Science

A new way of thinking about heredity, fertilization, and development was made possible by the work of botanists and those less formally engaged in botanical studies. For example, In Cell-Formation and Cell-Division (1875), Eduard Strasburger (1844–1912) described the division of plant cells and laid an important foundation for cell biology.

Many scientists were interested in theories of heredity in connection with Charles Darwin's (1809–1882) theory of evolution. But the work most closely associated with the development of modern genetics was based upon the study of plant hybridization. Joseph Gottlieb Koelreuter (1733–1806) was one of the first botanists to systematically make and test hybrids. Koelreuter's work was extended by Carl Friedrich von Gaertner (1772–1850).

IN CONTEXT: PALEOBOTANY

Paleobotany is the study of the plant life of the geological past. Paleobotany is pursued most often through the study of fossils, or impressions of plant parts that have been preserved in sedimentary rocks, coal, or other geological deposits. The most ancient plant fossils are older than one billion years, as is the case of microscopic impressions of Precambrian algae. There are also much younger fossils, as is the case of pollen in recently deposited lake sediments.

Objectives of paleobotany include the use of knowledge about fossil plants to infer the likely characteristics of their environments, including the type of climatic conditions under which they grew. Paleobotany endeavors to reconstruct past climates and regional vegetation systems by studying the fossilized remains of plants or preserved pollen samples. Such studies have yielded information regarding global climate change, both natural and man-made, and its effects on specific environments. Paleo-botanists aid in the identification of various climatic episodes. By combining geological evidence of glacial periods, or ice ages, with changes in regional flora, scientists have been able to create a more detailed picture of the development, course, and effects of such episodes.

Paleobotany is an essential branch of research on evolution. As early as 1790, some of the seminal research in evolutionary theory included botanical studies. Some of the primary goals of paleobotany are to discover the earliest appearances of various groups of plants and to understand the evolutionary relationships among them. Paleobotanists are also interested in the nature of the communities of fossil plants, and the species of animals with which they may have lived. Sometimes paleobotanical knowledge can be used for more practical purposes, such as assisting in the discovery of underground reserves of fossil fuels. Today paleobotany is utilized in a multitude of scientific settings, from archaeology to natural resource acquisition.

Paleobotanists commonly collect and identify microscopic spores, pollen, and bits of larger tissues. They also may identify larger, macroscopic plant remains such as leaves and even fossil tree trunks. Often, only the major plant group to which these plant parts belong, such as order or family, can be identified. In the case of more recent plant fossils that represent species that are still extant (not extinct), the remains may even be identifiable down to genus or species. Sometimes, the age of samples is known quite accurately. Paleobotanical studies of some recent lake sediments have shown that sediment layers sometimes develop as annual accumulations. The total number of layers can be subtracted from the current year to determine an age for the sequence or any layer within.

Palynology (the study of fossil spores and pollen) is an important subdiscipline of paleobotany, and can be used to illustrate the nature and breadth of paleobotanical research. Palynologists search samples of lake sediment, river sediment, or a bog peat of known age, carefully identifying and counting the microscopic pollen. Identification serves to place each specimen into whatever fossil group it belongs, down to the most specific level possible, which is often to the species.

From the assemblages of fossil pollen, palynologists make inferences about the types of forests or other plant communities that may have occurred in the local environment. These interpretations must be made carefully, however, because species are not represented in the pollen record in ways that directly reflect their abundance as mature plants. For example, pollen of wind-pollinated species is relatively abundant in lake sediments, whereas species that are insect pollinated are not well represented. Combining these sorts of observations and knowledge of the present, climatically-influenced distributions of these species, scientists can come to insightful conclusions about both the historical plant communities and past climates.

Palynologists sometimes work with archaeologists to study plants represented in archaeological deposits. Pollen samples are collected from geological strata or from artifacts, such as charcoal from the inside face of pottery, and they are then analyzed to determine what types of plants are present. Samples taken from geological strata yield clues about the settings in which prehistoric people lived. Similar samples taken from artifacts give researchers clues about prehistoric subsistence and farming patterns. For example, palynological studies provided the first scientific evidence of crop domestication, especially corn, in the Americas. Archaeologists have also used palynological research on past climates to determine which species of plants or crops were imported to certain areas through trade or conquest. This area of paleobotany is often known as paleoethnobotany, a special sub-discipline interested in the way past communities interacted with local flora and climates.

In the 1860s, Gregor Mendel (1822–1884) carried out a remarkable series of hybridization experiments and systematically analyzed the results of his tests. Mendel is generally regarded as the founder of modern genetics and the basic laws of genetics (segregation and independent assortment) are known as Mendel's laws. Although his work was ignored for almost 40 years, Mendel's laws were rediscovered at the beginning of the nineteenth century by Hugo de Vries (1848–1935), Carl Correns (1864–1935), and Erik von Tschermak (1871–1962).

Modern genetics can be seen as the result of the integration of three lines of investigation: classical breeding tests (many including plants), cytology, and biochemistry. Dramatic discoveries have been made in agriculture, and the impact of genetic research can be seen even at the corner grocery store. To eat or not to eat genetically engineered products is a question asked by many people after the Flavr Savr ™ tomato hit the

supermarkets in 1993. This variety of tomato contains a gene allowing it to remain firm longer during the ripening process, thus extending its shelf life. Many people, however, fear that genetically manipulated foods may have unexpected side effects for those who eat them.

Genome sequencing has been one of the scientific highlights of the last ten years, with complete sequences now existing for a number of microbes, as well as for eukaryotic organisms including rice (Oryza sativa). Naturally, the genome sequence that has received the most publicity is the articulation of the human genome, but advances in plant genetics also carry profound scientific and economic significance.

It would take many volumes to attempt to list the uses and contributions of botanical science to fundamental advances in biology and even seemingly distant physical sciences. For example dendrochronology, the dating of events and variations in environment in former periods by comparative study of growth rings in trees and aged wood (“proxy indicators” for past environmental variations) is, of course, highly dependent upon assumptions of tree growth derived from botanical study. Dendrochronology is an important technique in a number of disciplines, including archeology, paleontology, paleobotany, geomorphology, climatology, ecology, forensics, and even for dating art using wood. The morphological and cellular features of plants enable archeologists and paleontologists to more accurately date archeological sites because the cell wall of most plants—often with a size, shape, and pattern specific to individual plant species—is not easily digested and persists when other plant features are destroyed.

Modern Cultural Connections

Classification Continues

Plant classification systems depend upon observations from a diverse group of global scientists. Although controversies can occur, they are mediated and resolved by an international commission of scientists that employs the logical rules of scientific nomenclature to name newly discovered species or subspecies.

Modern molecular studies on plants have helped establish commonality above the classification of Kingdom. Three “Domains” divide living forms into the Domain Bacteria (modern bacteria plus cyanobacteria, also known as blue-green algae); Domain Archaea, comprised of “ancient bacteria” and some extremophiles, but generally described as prokaryotes lacking cell walls containing muramic acid (or cell walls at all); and Domain Eukarya (eukaryotes). The plant, animal, fungal, and several other kingdoms are all grouped under Domain Eukarya, that is, organisms having cells with nuclei, because they are more closely related to each other than members of the other kingdoms.

Ethnobotany

Many of the common drugs available in drugstores today have been developed from plants through the study of ethnobotany. The legendary American ethnobotanist and Harvard professor Richard Evans Schultes (1915–2001) defined ethobotany as “the study of human evaluation and manipulation of plant materials, substances, and phenomenon, including relevant concepts, in primitive or unlettered societies.”

Ethnobotanists explore how plants are used for food, shelter, medicine, clothing, hunting, and religious purposes. Many ethnobotanical projects are interdisciplinary efforts involving research from diverse fields such as anthropology, botany, medicine, pharmacology, and chemistry.

Although medicine and botany have a historically close relationship, as modern medicine and drug research have advanced, chemically-synthesized drugs have replaced plants as the basis of most medicinal agents in developed countries. Recently, however, problems with drug resistant microorganisms, side effects, and emerging diseases for which no medicines are available have brought attention to plants once again as a potential source of new therapeutic drugs. The 1990s were a renaissance period in ethnobotany, and many drug companies sponsored field research. Currently, 40–50% of available drugs have their origin in natural products.

Ethnobotanists play a key role in prospecting potential plants for useful compounds. They are like detectives who collect plant evidence in order to find active ingredients against illness. Plants are processed and tested by ethnopharmacologists, using state of the art laboratory equipment. The goal is to partition plants' metabolites to determine how relevant they are to the therapeutic areas of interest. Promising plant compounds are processed to obtain pure substances. These natural compounds are then compared to available therapeutics by laboratory testing. If these trials are successful, the compound is structurally characterized and is subjected to a confirmatory biological trial, then human trials. The discovery of a new drug is a long and expensive process. From the isolation of a substance to its availability at drugstores, the average drug pipeline can span a decade.

Tropical forests contain an extraordinary diversity of plant species. Many are still unknown, and many are unique and potentially useful as therapeutic sources. The value of biodiversity and the need to preserve the intact botanical resources of places like the Amazon is now widely recognized. Less broadly understood, but also endangered, is the knowledge of how these plants are used by local aboriginal peoples, whose customs and cultures are quickly vanishing.

Biologically diverse countries are generally poor, while wealthy drug companies have headquarters in developed nations. Rates of deforestation and extinction of species are the highest among poor nations. About 70% of world plant species evaluated in 2004 by The World Conservation Union (IUCN) are threatened with extinction. Conservationists and ethnobotanists fear that perhaps a key compound needed to cure AIDS or cancer has already been burned and replaced by crops or grass.

IN CONTEXT: FORENSIC BOTANY

Soil, plant fragments, and pollen, maybe in trace amounts, are often left behind at the scene of a crime. An expert in botany can often help unravel such evidence.

Soil and mud, in particular, are often present in footprints or tire tracks and can help link a suspect to the scene of a crime. Because soil is a mixture of mineral, plant, and animal matter that is often characteristic of a particular area, it may reveal something about a suspect's movements. The forensic botanist, first with the naked eye, looks at any soil or mud and assesses evidence of tell-tale plant debris.

Suspects and victims also, often unknowingly, carry various items of plant debris on their bodies and clothes such as flower petals, seeds, and pollen. These are often native to a specific area. For instance, if pine needles are found around a victim who seems to have perished in an area where there are no evergreens, it may tell the investigators something important and specific about the suspect and his or her movements. The botanist can investigate what species carries these particular needles and so help link the perpetrator to a specific area.

Pollen grains are tiny and are not usually noticed by those involved in a crime. Pollen is often found almost everywhere—in hair, on surfaces and on paper. If pollen is found on the envelope of a threatening letter or a ransom note, for instance, it may provide a valuable link to the suspect. There are pollen databases that can show the investigators where a particular pollen sample may have come from.

When a body is left out in the open or in a shallow grave, plant debris, including leaves and needles, may cover the remains. Analysis of this growth can often help establish the time and season of death and burial.

Another problem concerning ethnobotanists is the increase of bio-piracy (the appropriation of biological resources by foreign corporations or nations for economic gain). In recent years, through the advance of biotechnology, as well as the ease in registering international trademarks and patents, exploitation of poor countries through bio-piracy has bloomed. In order to stop such exploitation, it is necessary to offer incentives to preserve biodiversity and local cultural integrity. When commercial benefit is achieved, it is fundamental that international policies guarantee that countries where plant resources are found also benefit from the proceeds.

Critical New Roles

Botanists and botany also play an important part in monitoring climate change and in providing information critical to the creation of informed solutions, especially those designed to preserve biodiversity.

Wet tropical forests, harboring at least half of all known plant and animal species, are disappearing rapidly because of fire, selective logging, and clear-cutting. The Amazon forest is the richest region of biodiversity on the globe, comprising more than one third of all species according to the World Wildlife Fund. The Brazilian Amazon basin contains about 40% of the world's remaining tropical rainforest and plays vital roles in maintaining biodiversity, regional hydrology, climate, and carbon storage on Earth (from plants that remove carbon dioxide from the atmosphere). The area also suffers the world's highest absolute rate of deforestation; nearly 7,700 square miles (2 million hectares) per year were destroyed in the period from 1995 to 1999 alone.

The majority of the 2.7-million square miles of the Amazon basin is constituted by a dry land forest distributed alongside nine South American countries: Bolivia, Brazil, Colombia, Ecuador, French Guyana, Guyana, Peru, Suriname, and Venezuela. This forest never floods, and it is spread across a great plain that is relatively easy to destroy by fire. In recent decades, about 12% of this forest was destroyed, mostly from agriculture, timber harvesting, and mining. Due to the resultant poor soil, many scientists argue this area can become a great desert if this process continues.

Biological diversity in plant life is as critical as bio-diversity in animal life. Biodiversity helps maintain an evolving ecosystem. It is also an important source of genetic material for the development of new drugs. Pharmaceutical development from rainforest plant species could be an important source of funds for future development, which could ultimately serve as a means to protect environmental resources in the region. Parts of the Amazon Basin are among the most genetically diverse regions on the planet, and a wide variety of biological compounds discovered there have been patented by corporations around the world. One example is the anticancer drug Vincristine, which was originally extracted from a species of periwinkle found in the region.

See Also Biology: Classification Systems; Biology: Comparative Morphology: Studies of Structure and Function; Biology: Developmental Biology; Biology: Ecology; Biology: Genetics; Biology: Genetics, DNA, and the Genetic Code; Biology: Ontogeny and Phylogeny; Earth Science: Oceanography and Water Science.

bibliography

Books

Braziller, George. The Medieval Health Handbook. New York: Tacuinum Santatis, 1976.

Campbell, N., J. Reece, and L. Mitchell. Biology. 5th ed. Menlo Park: Benjamin Cummings, Inc. 2000.

Evans, Howard Ensign. Pioneer Naturalists. New York: Holt, 1993.

Heiser, Charles B. Of Plants and People. Norman: University of Oklahoma Press, 1985.

Morton, A.G. History of Botanical Science. London: Academic Press, 1981.

Porter, Roy. The Greatest Benefit to Mankind: A Medical History of Humanity. New York: W.W. Norton & Co., 1997.

Roth, Charles E. The Plant Observer's Guidebook. Englewood Cliffs, NJ: Prentice-Hall, 1984.

Siraisi, Nancy. Medieval and Early Renaissance Medicine. Chicago: Univ. of Chicago Press, 1990.

Web Sites

National Biological Information Infrastructure.

“Botany.” http://www.nbii.gov/portal/community/Communities/Plants,_Animals_&_Other_Organisms/Botany/ (accessed February 16, 2008).

Iuri D. Louro

Paulo B. Chaves

K. Lee Lerner

Brenda Wilmoth Lerner

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Biology: Botany." Scientific Thought: In Context. . Encyclopedia.com. 19 Nov. 2018 <https://www.encyclopedia.com>.

"Biology: Botany." Scientific Thought: In Context. . Encyclopedia.com. (November 19, 2018). https://www.encyclopedia.com/science/science-magazines/biology-botany

"Biology: Botany." Scientific Thought: In Context. . Retrieved November 19, 2018 from Encyclopedia.com: https://www.encyclopedia.com/science/science-magazines/biology-botany

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.