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 "Father of Botany" Palermo Botanic Gardens
The first steps in the history of botany would have been taken with the empirical plant lore passed from generation to generation in the oral traditions of our paleolithic hunter-gatherer ancestors. The written record of plants dates from the Neolithic Revolution as the domestication of plants and animals was established in settled agricultural communities around the world about 2,500 to 10,000 years ago. The first clear indication of a critical curiosity for plants themselves, rather than their uses, appears in the teachings of Aristotle’s student Theophrastus at the Lyceum in ancient Athens in about 350 BC. In Europe this early glimpse of botanical science was soon enveloped by the Middle Ages and a preoccupation with medicinal plants that lasted more than 1000 years during which the medicinal works of classical antiquity were reproduced again and again in manuscripts and books called herbals while in China and the Arab world, the Greco-Roman work on medicinal plants was carefully preserved and extended – but only as a medicinal record. The European Renaissance of the 14th – 17th centuries heralded a scientific revival during which botany gradually emerged from natural history as an independent science distinct from medicine and agriculture. Herbals were replaced by Floras, books that described the native plants of local regions. The invention of the microscope stimulated the study of plant anatomy and the first carefully designed experiments in plant physiology were performed. With the expansion of trade and exploration beyond Europe the many new plants being discovered were subjected to an increasingly rigorous process of description, classification and naming. From these beginnings have radiated the myriad contemporary plant sciences ranging from the applied fields of economic botany in its many forms (notably agriculture, horticulture and forestry), to the continued study of plants and their interaction with the environment over many scales from the large-scale global significance of vegetation and plant communities (biogeography and ecology) through to the small scale of cell theory and molecular biology.
[edit] IntroductionMain article: Outline of botany Botany (Greek Βοτάνη - grass, fodder; Medieval Latin botanicus – herb, plant)[1] and zoology together make up the core disciplines of biology (not named as such until the early 19th century) and the history of all these subjects is closely associated with that of the natural sciences chemistry, physics and geology. A distinction can be made between botanical science in a pure sense, as the study of the plants themselves, and botany as applied science, which relates more to the human use of plants (sometimes known as economic botany or ethnobotany). Early natural history divided pure botany into three main streams, morphology-classification, anatomy and physiology.[2] Most notable of the topics in applied botany are horticulture, forestry and agriculture but, less obviously, topics like weed science, plant pathology, floristry, pharmacognosy and others. However, over time there has been a progressive diversification and integration of disciplines with new subjects and combinations constantly arising. Modern molecular systematics, for example, includes the techniques of taxonomy, genetics, computer science and more. Within botany there are a number of subdisciplines focusing on special plant groups and each with their specific related studies of classification, morphology etc. Included here are: phycology (algae), pteridology (ferns), bryology (mosses and liverworts) and palaeobotany (fossil plants). Fungi now constitute their own kingdom so mycology, once a botanical discipline, is now placed elsewhere. [edit] Ancient and medieval knowledgeMain article: Neolithic Revolution It must be assumed that, of necessity, pre-literate nomadic hunter-gatherer societies by oral tradition passed on their empirical findings about plant kinds and their use as foods, poisons, medicines and so on. The nomadic life-style was drastically changed with the formation of settled communities in about twelve centres around the world during the Neolithic Revolution from about 10,000 to 2500 years ago. This marked the domestication of plants and animals, the emergence of the written word, along with increasingly sophisticated technology and the formation of the social structure of civilization as we define it today. [edit] Plant lore and plant selectionFurther information: Cultigen taxonomy and Herbal All staple foods were domesticated in prehistoric times. The staple foods of all continents involved the selection of better-yielding varieties in a selection process that would have taken hundreds to thousands of years – legumes on all continents, rice in East Asia, wheat and barley in the Middle east, and maize in Central and South America. Botanist William Stearn has pointed out that ”cultivated plants are mankind’s most vital and precious heritage from remote antiquity”.[3] During the Neolithic in about 3000 BC we have the first known illustrations of plants[4] and descriptions of gardens in Egypt.[5] However protobotany, the first pre-scientific written record of plants, did not begin with food; it was born out of the medicinal literature of Egypt, China, Mesopotamia and India.[6] As noted by Morton, agriculture was the occupation of the poor and uneducated while medicine was the influential realm of shamen, priests, apothecaries, magicians and physicians who were more likely to record their special magical knowledge for posterity.[7] [edit] Theophrastus and the origin of botanical scienceMain article: Theophrastus Ancient Greece of the 6th century BCE was a vibrant centre at the confluence of Egyptian, Mesopotamian and Minoan cultures and here there emerged a genuine non-anthropocentric curiosity about plants themselves rather than the uses that could be made of them. Philosophical thought of this period ranged freely through many subjects. Empedocles (490–430 BCE) foreshadowed Darwinian evolutionary theory in a crude formulation of the mutability of species and natural selection.[8] The physician Hippocrates (460– 370 BCE) approached healing by close observation and the test of experience. The botanical works of the day extended beyond the description of medicinal plants to the topics of plant geography, morphology, physiology, nutrition, growth and reproduction.  Fresco in Apostolic Palace, Rome, Vatican City, by Raphael 1509-1510 Greek pharmacology was synthesised in Materia Medica c. 60 CE by Pedanius Dioscorides (c. 40-90 CE) and this account was to decide the general form of every ancient and most modern herbals, both oriental and occidental until the Renaissance being the most widely copied medical text.[9] Though rich in medicinal information with descriptions of about 600 medicinal herbs, the botanical content was nevertheless brief.[10] Theophrastus of Eressus (Greek: Θεόφραστος; c. 371 – 287 BCE), often referred to as the ”Father of Botany”, was a student and friend of Aristotle (384–322 BCE), co-founder of biological science, and successor to Aristotle as head of the Lyceum (a place of learning like a modern university) in Athens with its tradition of peripatetic philosophy. The Lyceum prided itself in a tradition of systematic observation of causal connections, critical experiment and rational theorizing. Theophrastus challenged the superstitious medicine of the physicians of his day, called rhizotomi, and also the control over medicine exerted by priestly authority and tradition. In the garden at the Lyceum were many plants collected in distant lands and here he gained much of his knowledge of plants.[11]. With Aristotle he had tutored Alexander the Great whose military conquests were carried out with all the scientific resources of the day, and the Lyceum garden probably contained many botanical trophies from his camapaigns.[12] Theophrastus's major botanical works were the Enquiry into Plants and Causes of Plants which were his lecture notes for the Lyceum.[13] The opening sentence of the Enquiry is like a botanical manifesto: “We must consider the distinctive characters and the general nature of plants from the point of view of their morphology, their behaviour under external conditions, their mode of generation and the whole course of their life”. The Enquiry deals with the forms and classification of plants, and with economic botany, examining the techniques of agriculture (relationship of crops to soil, climate, water, habitat) and horticulture. His other book Causes of Plants covers plant growth and reproduction (akin to modern physiology) in which he distinguishes between monocotyledons and dicotyledons[14] He often included descriptions of habitat and geographic distribution with his plant descriptions.[15] Like Aristotle he grouped plants as "trees", "shrubs" and "herbs" but also distinguished annuals, perennials and biennials, the difference between determinate and indeterminate inflorescences, also details of floral structure including fusion of petals, position of the ovary and more. In these works we have the first clear exposition of the rudiments of plant anatomy, physiology, morphology and ecology — presented in a way that would not be matched for another eighteen centuries.[16] Roman encyclopaedist Pliny the Elder (23–79 CE) in his influential Naturalis Historia deals with plants in Books 12 to 26 of his 37-volume work and frequently quotes Theophrastus but with little botanical insight. He nevertheless makes a distinction between true botany on the one hand, and farming and medicine on the other.[17] The Romans though contributing little to the foundations of botanical science laid by the Greeks nevertheless dealt in detail with agriculture as an applied science (in works titled De Re Rustica) through the writers Cato the Elder (234–149 BCE), Marcus Varro (116–27 BCE) and, in particular, Columella (CE 4–70).[18] [edit] Medicinal plants of the Middle AgesChina was on a similar technological trajectory Chinese philosophy was developing along with the Greek. The Chinese dictionary Erh Ya included about 334 plants classed as trees or shrubs with a common name and described and illustration had become common by 400 AD. As Europe entered the Middle Ages, a period of disorganised feudalism and indifference to learning, China and the Arab world did not do the same. Between AD 100 and 1700 many new works on pharmaceutical botany were produced, encyclopaedic accounts and treatises produced from the imperial court. They were free of superstition and myth. There was a high level of description, naming, culture, economic and medicinal uses, even elaborate monographs on ornamental plants. But there was no experimental method, sexual system, nutrition, or anatomy. In the West, after Theophrastus, botany passed through a period of 1800 years when little progress was made and, indeed, many of the early insights were lost. The 400-year period from the 9th to 13th centuries C.E. was also the Islamic Golden Age or Islamic Renaissance when Islamic culture and science thrived. The Greco-Roman texts were preserved, copied and extended although the attention given to plants always emphasised their medicinal properties. [edit] The Age of HerbalsMain article: Herbal  In the Middle Ages, agriculture occupied 90% of the European population. Nevertheless, the 15th and 16th centuries was the Age of the European Herbals (aided by the advent of printing with movable type and the use of woodcut illustrations), not treatises on agriculture.[19] Authors of herbals were often curators of gardens.[20] Herbals were created primarily from a utilitarian desire to make use of plants rather than study them for their own interest: most were derivative compilations from the classics, notably the De Materia Medica of Pedanius Dioscorides. However here were the beginnings of descriptive botany and the modern Flora. German Otto Brunfels' (1464-1534) Herbarum Vivae Icones (1530) contained accurate illustrations and about 47 species that were new to science. His fellow countryman Hieronymus Bock's (1498-1554) Kreutterbuch of 1539 described plants found in the woods and fields, which were illustrated in the 1546 edition.[21] However, it was Valerius Cordus (1515-1544) who pioneered the formal botanical description including both flowers and fruits, anatomical details including the number of chambers in the ovary, and the type of ovule placentation. He also made observations on pollen and distinguished between inflorescence types.[22] His work, the 5 volume Historia Plantarum, was published by Swiss Conrad Gesner in 1561-1563, about 18 years after his early death aged 29. Similarly Rembert Dodoens (1517-1585) in Stirpium Historiae (1583) included descriptions of many new species from the Netherlands in a scientific arrangement.[23] In England William Turner (1515-1568) in his Libellus De Re Herbaria Novus (1538) published names, descriptions and localities of many British plants. [edit] Botanical gardens and herbaria  Both public and private gardens form a constant background to the unfolding of botanical science. Many plants in herbals were garden plants and the herbalists often directors or associates of botanic gardens with a role as “scientific gardener”. Early botanical gardens were physic gardens, repositories for medicinal simples or officinals. By the eighteenth century the physic gardens had been transformed into "order beds" that demonstrated the classification systems that were being devised by botanists of the day, their modern day equivalents being known as "systems gardens". But very soon botanical gardens changed once again as botanical and horticultural exploration overseas accumulated trophies of curious, beautiful and new plants to be displayed in these gardens. The first botanical gardens of the modern tradition were established in northern Italy, starting with Pisa (1544), founded by Luca Ghini (1490-1556); they were generally associated with universities or other institutions where the plants could be studied. Collections of dried specimens were called herbaria (book of plants) and accumulating plants in this way dates from the sixteenth century[24]. Buildings called herbaria stored pressed and dried plants mounted on card with descriptive labels: these could be preserved in perpetuity stored in cupboards in systematic order and this allowed the exchange of specimens with other institutions, a technique of descriptive and systematic botany that has been used ever since. There was, also at this time, a recognition of the need for accurate botanical illustrations indicating the diagnostic features of plants.[25] [edit] Botany and the Renaissance 1550–1800The Renaissance resulted in a reinvigorated botany as the church, feudal aristocracy and an increasingly influential merchant class that supported science and the arts, jostled in a world where exploration swelled the large public and private gardens with plant trophies and introduced an eager population to novel crops and drugs from the New World, Asia and the East Indies. Botany in 17th C became an independent science as university botanical gardens, scientific organizations including acclimatization societies, specialized and subdivided the subject. All this along with a renewed interest in native plants and local flora heralded a new phase of description and identification. [edit] Botanical exploration: from herbal to FloraFurther information: Plant geography and Flora The seventeenth century marked the beginning of experimental botany and a more rigorous scientific method. The microscope launched the new discipline of plant anatomy where Grew and Malpighi established the foundations that would last for 150 years. Jung developed a descriptive terminology.[26] Meanwhile descriptive accounts of plants in foreign lands continued – for the West Indies (Hans Sloane (1660–1753)), China (James Cunningham); and the Moluccas (George Rumphius (1627–1702)). Exploration continued with collections for herbaria and new descriptions in China and Mozambique (João de Loureiro (1717-1791)), West Africa (Michel Adanson (1727–1806)) who devised his own classification scheme and forwarded a crude theory of the mutability of species; (Joseph Banks (1743–1820) visited Canada, did a circuit of the world with Captain James Cook (1728–1779), in 1772 Hebrides and Iceland.[27] Even so, the motivation for collecting in woods, fields and foreign lands was, in the first instance, medicinal. [edit] Classification and morphologyFurther information: List of systems of plant taxonomy, Plant taxonomy, and History of plant systematics  Plant classification can be divided into for historical phases, the form system, the sexual system, early and late natural systems, and contemporary systems.[28] Italian Andrea Caesalpino (1519-1603) studied medicine and taught botany at the University of Pisa for about 40 years eventually becoming Director of the Botanic Garden of Pisa from 1554 to 1558. His 16–book De Plantis(1583) describes 1500 plants and his herbarium of 260 pages and 768 mounted specimens still remains. Caesalpino moved away from characters of form and habit to those of flower and fruit including the structure and morphology of seeds; he also concept of the genus.[29] He was the first to try and derive principles of natural classification reflecting real relationships and he produced a classification scheme well in advance of its day.[30] Gaspard Bauhin produced two influential publications Prodromus Theatrici Botanici (1620) and Pinax (1623). These brought order to the 6000 species described and included synonyms. In the latter he used an abbreviated naming system with binomials and synonyms which foreshadowed Linnaeus' later standardization of this system. He also insisted that taxonomy should be based on natural affinities.[31]  It was Joachim Jung (1587–1657) who established a widely accepted terminology for plant parts including root, stem, leaf, flower, fruit and seed, as well radial and asymmetric flowers, although it was Joseph de Tournefort (1656–1708) who emphasized the morphology of flower and fruit as key characters for classification while at th same time reviving the ideas of genus and species. English botanist John Ray (1623–1705) built on Jung’s work to establish the most elaborate and insightful classification system of the day.[32] His observations started with the local plants of Cambridge where he lived, with the Catalogus Stirpium circa Cantabrigiam Nascentium (1860) which later expanded to his Synopsis Methodica Stirpium Britannicarum, essentially the first British Flora. Although his Historia Plantarum (1682, 1688, 1704) provided a step towards a world Flora as he included more and more plants from his travels, first on the continent and then beyond. He extended Caesalpino’s natural system with a more precise definition of the higher classification levels deriving many modern families and he thought that all parts of plants were important in classification. He was also among the first experimental physiologists. The Historia Plantarum can be regarded as the first botanical synthesis and text book for modern botany. His family system was later extended by Pierre Magnol (1638–1715).[33] According to botanical historian Morton, Ray "influenced both the theory and the practice of botany more decisively than any other single person in the latter half of the seventeenth century".[34] By the middle of the eighteenth century, the era of exploration and its vast botanical booty accumulating in gardens and herbaria was in dire need of listing and synthesis. It was Swede Carolus Linnaeus (1707–1778) who set about this task. He adopted a sexual system of classification using stamens and pistils as important characters. Among his most important publications were Systema Naturae (1735), Genera Plantarum (1737), and Philosophia Botanica (1751) but it was in his Species Plantarum (1753) that he gave every species a binomial thus setting the path for the future accepted method of designating the names of all organisms. His sexual system was later elaborated by Bernard de Jussieu (1699–1777) whose nephew Antoine-Laurent de Jussieu (1748–1836) extended yet again to include about 100 orders (present-day families).[35] Frenchman Michel Adanson (1727–1806) in his Familles des Plantes (1763, 1764), apart from extending the current system of family names, emphasized that a natural classification must be based on a consideration of all characters, even though these may be later given different emphasis: this method has, in essence, been followed to this day.[36] Eighteenth century plant taxonomy bequeathed to the nineteenth century clear ideas of the genus and species, a precise binomial nomenclature, and a system of classification based on natural affinities. [edit] Microscopy, anatomy and physiology In the first half of the eighteenth century botany was still preoccupied with the core business of description, diagnosis, classification and nomenclature but the field of investigation was beginning to widen. The microscope was invented in 1590 but it was only in the late 17th century that lens grinding by Antony van Leeuwenhoek gave the resolution needed to make major discoveries. General biological observations were made by Robert Hooke (1635–1703) but the solid foundations of plant anatomy were laid by Italian Marcello Malpighi (1628–1694) in his Anatome Plantarum (1675) and Englishman Nehemiah Grew (1628–1711) in his The Anatomy of Plants Begun (1671) and Anatomy of Plants (1682). These botanists had analysed and illustrated what we would now call developmental anatomy and morphology, tracing the process from seed to mature plant while with major observations concerning the stem and wood formation, while discovering and naming parenchyma and stomata along the way.[37] In plant physiology, following discoveries on the circulation of the blood, similar theories were canvassed on the movement of sap and the absorption of substances through the roots. Jan Helmont (1577–1644) by experimental observation and calculation, noted that the increase in weight of a growing plant cannot be derived purely from the soil, and concluded it must relate to water uptake.[38] Englishman Stephen Hales (1677–1761) established by quantitative experiment that there is uptake of water by plants and a loss of water by transpiration and that this is influenced by environmental conditions: he distinguished “root pressure, “leaf suction” and “imbibition” and also noted that the major direction of sap flow in woody tissue is upward. His results were published in Vegetable Staticks (1727) He also noted that “air makes a very considerable part of the substance of vegetables”.[39] English chemist Joseph Priestly (1733–1804) is noted for his discovery of oxygen (as now called) and its production by plants. Later Jan Ingenhousz (1730–1799) observed that only in sunlight do the green parts of plants absorb air and release oxygen, this being more rapid in bright sunlight while, at night, the air (CO2) is released from all parts. His results were published in Experiments upon vegetables (1779) and with this the foundations for twentieth century studies of carbon fixation were laid. From his observations he sketched the cycle of carbon in nature even though the composition of carbon dioxide was yet to be resolved.[40] Studies in plant nutrition had also progressed. In 1804 Nicolas-Théodore de Saussure's (1767–1845) Recherches Chimiques sur la Végétation was an exemplary study of scientific exactitude that demonstrated the similarity of respiration in both plants and animals, that the fixation of carbon dioxide includes water and that just minute amounts of salts and nutrients (which he analysed in chemical detail from plant ash) have a powerful influence on plant growth. [edit] Plant sexualityFurther information: Plant sexuality and Alternation of generations  Unravelling the reproductive mechanisms in mosses, liverworts and algae involved both uncertainty and conflict. In his Vergleichende Untersuchungen of 1851 Wilhelm Hofmeister (1824–1877) starting with the ferns and bryophytes demonstrated the process of sexual reproduction in plants as an “alternation of generations” between sporophytes and gametophytes.[41]. This initiated the new field of comparative morphology which, largely through the work of William Farlow (1844–1919), Nathanael Pringsheim (1823–1894) and Celakowski (1834–1902), Frederick Bower and Eduard Strasburger put on sound foundations the fact of alternation of generations throughout the vegetable kingdom.[42] However, it was Rudolf Camerarius (1665–1721) who was the first to establish plant sexuality conclusively by experiment. He declared in a letter to a colleague dated 1694 and titled De Sexu Plantarum Epistola that “no ovules of plants could ever develop into seeds from the female style and ovary without first being prepared by the pollen from the stamens, the male sexual organs of the plant".[43]  It was some time before German academic natural historian Joseph Kölreuter (1733–1806) extended this work by noting the function of nectar in attracting pollinators and the role of wind and insects in pollination. He also produced deliberate hybrids, observed the microscopic structure of pollen grains and how the transfer of matter from the pollen to the ovary inducing the formation of the embryo.[44] One hundred years after Camerarius, in 1793, Christian Sprengel (1750–1816) broadened the understanding of flowers by describing the role of nectar guides in pollination, the adaptive floral mechanisms used for pollination, and by demonstrating that cross-pollination was the rule, even though male and female parts are usually together on the same flower.[45] [edit] Nineteenth century foundations of modern botanySpecialists journals had started to appear in the late 18th century and from 1840 there was a shift in work practices from the production of weighty tomes by authoritative individuals and "gentlemen scientists", to the publication of “papers” that emanated from research “schools” that promoted the questioning of conventional wisdom.[46] Botany was greatly stimulated by the publication of the first “modern” text book, Matthias Schleiden's (1804–1881) Grundzuge der Wissenschaftlichen, published in English in 1849 as Principles of Scientific Botany which moved away from taxonomy and plant description as the primary focus of botanical research.[47] By 1850 an invigorated organic chemistry had revealed the structure of many plant constituents.[48] The great era of plant classification had now passed but the work continued. Augustin de Candolle (1778-1841) was successor to Antoine-Laurent de Jussieu and he edited the massive Prodromus Systematis Naturalis Regni Vegetabilis (1824-1841) with 34 other authors: it contained all the dicotyledons known in his day, some 58000 species in 161 families, and he doubled the number of recognized plant families, the work being completed by his son Alphonse (1806-1893) in the years from 1841 to 1873.[49] [edit] Plant geography and ecologyFurther information: Ecology and Plant community  Physiological plant geography, perhaps more familiarly termed ecology, emerged out of floristic biogeography in the late nineteenth century as the environmental influence on plants achieved greater recognition. Early work in this area was synthesised by Copenhagen professor Eugenius Warming (1841–1924) in his book Plantesamfund (Ecology of Plants) including new ideas on plant communities, their adaptations and environmental influences and this was followed by another grand synthesis, the Pflanzengeographie auf Physiologischer Grundlage of Andreas Schimper (1856–1901) in 1898 (published in English in 1903 as Plant-geography upon a physiological basis translated by W.R. Fischer, Oxford: Clarendon press, 839 pp.)[50] Ecology has recently become a combined effort of systematists, physiologists and geneticists. The opening of the nineteenth century marked an increase in interest in the connection between climate and plant distribution.[51] Carl Willdenow (1765–1812) examined the connection between seed dispersal and distribution, the nature of plant associations and the impact of geological history. He noticed the similarities between the floras of N America and N Asia, the Cape and Australia, and he explored the ideas of “centre of diversity" and "centre of origin”. German Alexander von Humbolt (1769–1859) and Frenchman Aime Bonpland (1773–1858) published a massive 30 volume work of their travels; Robert Brown (1773–1852) noted the similarities between the floras of S Africa, Australia and India while Joakim Schouw (1789–1852) explored more deeply than enyone else the influences of temperature, edaphic factors, soil water and light and this was supplemented by work of Alphonse de Candolle (1806–1893). Joseph Hooker (1817–1911) pushed the boundaries of floristic studies with his studies of the floras of Antarctica, India and the Middle East while also discussing the phenomenon of endemism. August Grisebach (1814–1879) in Die Vegetation der Erde (1872) examined physiognomy in relation to climate and in America geographic studies wee pioneered by Asa Gray (1810–1888). [edit] Developmental morphology Johann Goethe (1749–1832) was a supreme intellect of his day with his interests and influence extending into botany. In ‘’Die Metamorphose der Pflanzen’’ (1790) he attempted to provide a theory of plant morphology (he coined the word ‘’morphology’’) and in this publication his view of “metamorphosis” included modification during evolution, linking comparative morphology with phylogeny: it also stimulated discussion and research on the origin and function of floral parts[53] and this no doubt stimulated the opposing forces of German botanists Alexander Braun (1805–1877) and Matthias Schleiden investigating the principles of growth and form that were later extended by Augustin de Candolle (1778–1841). Until the 1860s the prevailing belief was the constancy of species, that each form was the result of an independent act of creation and therefore absolutely distinct and immutable. But the hard reality of geology and fossils needed explanation. Charles Darwin’s Origin of Species (1859) replaced this assumption with the theory of descent with modification. Phylogeny became a new principle and physiology thrived. Wilhelm Hofmeister established that there was a more or less uniform plan of organization running through all plants expressed through the alternation of generations and extensive homology of structures.[54] Julius von Sachs pioneered studies of protoplasm and its continuity through cell walls; chlorophyll; movement and ecology [edit] Anatomy and cytologyFurther information: Plant anatomy and Cell theory Plant anatomy studies on the stele were consolidated by Carl Sanio (1832–1891) who studied the secondary tissues and meristem including cambium and its action. All this and more was synthesized in the encyclopaedic comparative anatomy of Heinrich Anton de Bary in 1877. A synthesis of the stele in root and stem was completed by Van Tieghem (1839–1914) and of the meristem by Karl Nägeli (1817–1891). To these findings can be added extensive studies on the origins of the carpel and flower that continue to the present day.  Recognition of the overall cellular structure of organisms, with each cell possessing all the characteristics of life, is attributed to the combined efforts of botanist Matthias Schleiden and zoologist Theodor Schwann (1810–1882) in the early nineteenth century. Between 1870 and 1880, through the collective work of many researchers, it was determined that a nucleus is never formed anew but always derived from the substance of another nucleus and in 1882 Flemming observed he longitudinal splitting of chromosomes in the dividing nucleus and concluded that each daughter nucleus received half of each of the chromosomes of the mother nucleus. Then by the early 20th century it was clear that the number of chromosomes in a given species is constant. With genetic continuity confirmed and the finding by Eduard Strasburger that the nuclei of reproductive cells (in pollen and embryo) have a reducing division (halving, now known as meiosis) the field of heredity was opened up. By 1926 Thomas Morgan was able to outline a theory of the gene and its structure and function. The form and function of plastids received similar attention, the association with starch being noted at an early date.[55] Other workers showed that all cells come from the division of other cells and with the study of cell division and analysis of the structure of protoplasm and the cell wall, and the structure and function of the nucleus (which had been discovered by Robert Brown in 1831), plastids and vacuoles – what become known as cytology, or present-day cell theory was established. [edit] Photosynthesis, carbon and nitrogen fixation, water relations and nutritionFurther information: Soil plant atmosphere continuum and Photosynthesis  At the start of the 19th century the notion that plants could establish almost all their tissues from atmospheric gases was still poorly understood. It was only in 1882 that Sachs confirmed carbohydrates as the starting point for all other organic compounds in plants.[56] Chlorophyll was named in 1818 and its chemistry gradually resolved to early twentieth century. The mechanism of photosynthesis remained a mystery until the mid 19th century when Sachs, in 1862, noted that starch was formed in green cells only in the presence of light. The connection with chlorophyll pigment was made in 1864. Determining the precise biochemical pathway of starch formation did not begin until about 1915. The energy aspect of photosynthesis, whereby energy from the Sun is fixed in chemical form, and the dependence of all forms of life on this fixed energy, emerged in 1847 by Julius Rob. Mayer.[57] During the nineteenth century German scientists led the way in the production of a unitary theory of the structure and life-cycle of plants. Following improvements in the microscope at the end of the 18th century, Charles Mirbel (1776–1854) in 1802 published his Traité d'Anatomie et de Physiologie Végétale and Johann Moldenhawer (1766–1827) published Beyträge zur Anatomie der Pflanzen (1812) in which he describes techniques to separate the cells from the middle lamella layer that separates them. He identified vascular and parenchymatous tissues, described vascular bundles, observed the cells in the cambium, and interpreted tree rings. He found that stomata were composed pairs of cells, rather than a single cell with a hole. Although Moldenhawer is not credited with the cell theory accredited to Schleiden and Schwann,[58] his work demonstrated that plants were wholly cellular with each cell having its own wall. Work in anatomy leading up to 1850 was summarized by Hugo von Mohl (1805–1872) in Die Vegetabilische Zelle (1851) who also explored solute transport and the theory of water uptake by the roots using cohesion, transpirational pull, capillarity and root pressure.[59] To this list of German achievement can be added the definitive textbook on plant physiology synthesising the work of this period, Sach's Vorlesungen über Pflanzenphysiologie of 1882. Non-German advances were made in the early exploration of geotropism (the effect of gravity on growth) by Englishman Thomas Knight, together with the discovery and naming of osmosis by Frenchman Henri Dutrochet (1776–1847).[60] Significant discoveries relating to nitrogen assimilation and metabolism, including ammonification, nitrification and nitrogen fixation (the uptake of atmospheric nitrogen by symbiotic soil microorganisms) had to wait for advances in chemistry and bacteriology in the late nineteenth century and this was followed in the early twentieth century by the elucidation of protein and amino-acid synthesis and their role in plant metabolism. With this knowledge it was now possible to outline the global nitrogen cycle.[61] [edit] Twentieth century Twentieth century science grew out of solid foundations laid in the 19th century. Research funding became available from agriculture and industry. By 1910 experiments using labelled isotopes were being used to elucidate plant biochemical pathways, to open the line of research leading to gene technology. There was now an awareness of the unity of structure and function at the cellular and molecular levels of organisation. At the level of communities it would take until mid century to consolidate work on ecology and population genetics.[62] [edit] MoleculesMain article: Molecular biology In 1903 Chlorophylls a and b were separated by chromatography and through the 1920s and 1930s biochemists, notably Hans Krebs (1900-1981) and Carl (1896–1984) and Gerty Cori (1896–1957) began tracing out the central metabolic pathways of life and between the 1930s and 1950s the role of ATP as the chemical energy source in the cell located in mitochondria was established. From the 1930s the detail of the constituent reactions of photosynthesis were progressively revealed and by 1944 DNA had been extracted.[63] Another remarkable discovery was that of plant hormones or “growth substances”, notably auxins, gibberellins and cytokinins.[64] as well as photoperiodism (control of plant processes, especially flowering, by relative lengths of day and night).[65] Following the establishment of Mendel’s laws, the gene-chromosome theory of heredity culminated with the work of August Weismann who identified the chromosomes of the nucleus as the hereditary material and noted the halving of the chromosome number in germ cells, anticipating the details of meiosis In the 1920s and 1930s population genetics, unified the idea of evolution by natural selection with Mendelian genetics producing the modern synthesis. By the mid-1960s the molecular basis of metabolism and reproduction was sound and the new science of molecular biology thriving. Genetic engineering, the insertion of genes into a host cell for cloning, began in the 1970s with the invention of recombinant DNA techniques and commercial applications followed in the 1990s especially in relation to agricultural crops. [edit] Computers, electron microscopes and evolutionFurther information: Ultrastructure and Palynology  Mid-century transmission and scanning electron microscopy presented another level of resolution to the structure of matter, taking anatomy into the world of “ultrastructure”.[66] Taxonomy using mostly floral characters was now being supplemented by new techniques including pollen morphology, embryology, anatomy, cytology, serology, macromolecules and more.[67] The emergence of the PC facilitated the development of numerical taxonomy (also called taximetrics or phenetics) for the rapid analysis of comparative data and attempts to create truly natural phylogenies have spawned the disciplines of cladistics or phylogenetic systematics, now incorporating molecular data to become molecular systematics. In 1936 Alexander Oparin (1894–1980) had demonstrated how organic matter could be synthesized from inorganic and in the 1960s it was found that the Earth’s first plants, the cyanobacteria called stromatolites, dated back some 3.5 billion years.[68] [edit] Biogeography and ecologyMain article: Biogeography Alfred Wegener's (1880– 1930) theory of continental drift was not fully developed until 1912. This eventually gave additional impetus to comparative physiology and the study of biogeography[69] while ecology was now making a major contribution, ideas of the 1930s including those of the plant community, succession, influences on community change and energy flows.[70] Nikolai Vavilov (1887–1943) produced extensive accounts of the geography, centres of origin, and evolutionary history of economic plants. The cytological basis of the gene-chromosome theory of heredity extended from about 1900–1944 and was initiated by the rediscovery of Gregor Mendel's (1822–1884) laws of plant heredity first published in 1866 in Experiments on Plant Hybridization and based on cultivated pea, Pisum sativum: this heralded the opening up of plant genetics. The cytological basis for gene-chromosome theory was explored through the role of polyploidy and hybridization in speciation and it was becoming better understood that interbreeding populations were the unit of adaptive change in biology.[71]  Ecology became an independent discipline in the 1940s and 1950s after Eugene Odum (1913–2002) synthesized many of the concepts of ecosystem ecology, placing relationships between groups of organisms (especially material and energy relationships) at the center of the field. [edit] Twenty-first centuryAt the beginning of the 21st century the “web” has modified work practices as scientific journals and new research becomes progressively available online. The biological and physical sciences continue to integrate as new technology and insights become available to all fields – biology and maths to biometrics, biology and physics to biophysics, computer science, genetics and phylogenetic systematics combined into molecular systematics – and so on. The distinction between pure and applied research is now blurred as work at the molecular level through to modern ecology translates into the applied botanical science needed to tackle large-scale global issues of resource management, conservation, food security, biologically invasive organisms, carbon sequestration and sustainability. [edit] See also
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