BOTANY. — Botany, or plant physiology, is the science of plants. Plants are considered under three main aspects: morphological, physiological, and systematic.
There are several chapters within *morphology*, or the study of form: *cytology*, which deals with the structure of individual cells; *histology*, or the study of tissues; anatomy, which, by recognizing the distribution of different types of tissues in the plant, establishes the internal structure of individual organs; *organography*, which describes the external form of plants and their organs; and finally, chapters concerning the cytology of reproduction, *embryology*, etc.
The chapters of *physiology*, or the study of functions, are even more numerous.
The life of plants proceeds with a continuous intake of materials, most of which have nutritional significance. Unlike animals, which can only nourish themselves with organic substances, plants typically have the capacity to nourish themselves with mineral substances. Once these substances are introduced into the plant body, they are first transformed, through a series of chemical reactions, into organic compounds; subsequently, through further modifications, they are, to a greater or lesser extent, organized—that is, transformed into living substance or protoplasm.
The series of transformations undergone by materials introduced into the plant does not stop here, since the various phenomena accompanying life cause a continuous wear and tear of living substance and, consequently, a continuous breakdown of its constituents, which are further transformed with a tendency to revert to an inorganic state. Living cells, however, contain numerous compounds—some still organic, others mineral—which, having the value of waste substances, are eliminated. Other materials, having reached an organic form and before being organized, undergo partial or even no breakdown and are likewise eliminated, either permanently or temporarily.
The mineral substances themselves taken up by plants may not be utilized and may be eliminated without having undergone any organizational processes. Thus, there is a complex exchange of substances with the external environment during the life of plants, which constitutes the subject of study of a major branch of physiology dedicated to *material exchange or metabolism* (q.v.). In this, we distinguish an ascending or synthetic phase (*anabolism*), which, through processes of *organization*, leads to the formation of compounds with more or less complex molecules, such as those that participate in the constitution of living matter; and a descending or analytical phase (*catabolism*), which, through inverse processes, leads to the appearance of waste substances, sometimes with extremely simple molecules.
Among the processes studied in the various chapters of the physiology of material exchange are those concerning the physiology of water uptake, its dispersion, and transport; the physiology of mineral nutrition; the *organization* of carbon through photosynthesis and chemosynthesis; the *organization* of nitrogen; the processes of organization; the study of the products of assimilation; the modes of elimination and the nature of the substances eliminated, etc.
Parallel to material exchange, plants also undergo an *energy exchange*.
The *organization* of carbon in green plants is made possible by their ability to utilize the radiant energy of sunlight, and a significant portion of the products of this process constitutes a reserve of energy in the plants. Indeed, with the breakdown of these compounds, the same amount of energy that was taken from light for their synthesis is released and used in the course of many other reactions. These breakdown processes, or *dissimilation*, occur in different ways and with or without the intervention of molecular *oxygen* from the *outside*; thus, we have the groups of phenomena known as *aerobic respiration*, *intramolecular respiration*, and *fermentations*.
Other branches of physiology include those concerning *growth* (seed germination, the ways in which internal and external factors influence growth, growth movements and the orientation of plants, the conformation of plants, and the factors that determine it; *teratology*, or the study of abnormal forms, etc.); *development*, i.e., the ways in which, over the course of its life, the plant acquires new properties leading to reproduction and death; the *physiology of sexuality* and *reproduction*; the mechanism of the *transmission of hereditary characters*, both from a cytological and functional standpoint; the *movements of plants*; and *ecology*, i.e., the study of the relationships between plants and their external environment, as well as the structural and physiological modifications that environmental characteristics induce in them.
Of special botany, the branch perhaps best known to laypeople is *systematics* or *taxonomy*, which alone or almost alone represented the entire field of botany in antiquity and the Middle Ages. The aim of systematics is the knowledge of all plants and their distribution in a scheme that, while allowing for practical recognition (*classification*), corresponds to certain scientific requirements.
The first task of systematics is to establish the categories into which different plants are to be distributed or grouped; the most fundamental of these categories is the *species*, an entity that, although recognized early by scientists, has become increasingly difficult to define and circumscribe within natural limits as science has advanced, so much so that innumerable discussions have arisen and continue to arise regarding the value of this systematic category and its actual existence. Without entering into details here, it must be noted that the importance of these discussions is all the greater because their outcome determines whether to accept or reject the principle of the fixity or mutability of living forms, whether to embrace the creationist connection of individual species or the evolutionary theory, and the very orientation of science regarding a host of problems pertaining to the origin of life on earth that extend into the philosophical and transcendental realm.
Other systematic categories, of increasingly general scope, are genus, family, order, class, and division.
The result of such work of grouping and classifying into categories with ever more general similarities is the creation of a general scheme in which each form is assigned a specific position. Naturally, depending on the characters chosen for their construction, the value of such schemes will vary greatly, and the progress of systematics from antiquity to the present has consisted precisely in the progressive search for guiding characters that allow the construction of a natural system or scheme, in which plants are distributed based on their natural affinities.
Here again, scientific and philosophical problems intersect, as it is a matter of determining whether the affinity of different plant forms is such as to suggest a monophyletic origin—from a single ancestral archetype—or a polyphyletic origin.
The principal characteristics upon which modern systematics is founded are given by the comparative study of the mechanism of reproduction, the structure and function of the sexual organs, the embryology of the various forms, and their ontogenetic cycle.
Auxiliary disciplines of systematics, and also part of the special botany, are phytopaleontology and phytogeography.
The task of the first is the knowledge of plant forms that lived in other geological areas, while the second, based on ecological and karyological foundations and utilizing geological and climatological data, aims to explain the floristic composition of the different zones of the earth and their individual territories.
Another major branch of special botany is applied botany, whose main chapters are agricultural botany, forest botany, horticultural botany, phytopathology, pharmacognosy, etc.
The interest of such a vast and complex discipline as botany is evident; like the study of animals, the study of plants transcends human aspiration for knowledge as an end in itself, for it is a study of life, its origin, its manifestations, and its essence. From a certain point of view, moreover, the study of plant organisms is of greater interest than that of animals, the reason being that plants alone are autotrophic organisms while animals are heterotrophic. Plants alone, in other words, are capable of nourishing themselves with substances in the mineral state, whereas animals, lacking this capacity, are obliged to make use of materials already made organic by plants.
All animal life thus appears dependent on plant life, and the life of animal organisms on earth is rendered possible, so to speak prepared, by the necessarily more ancient existence of plants.
The knowledge of the processes by which plants organize carbon, nitrogen, sulfur, and phosphorus accordingly acquires an interest that transcends the mere botanical aspect, or even the biological aspect in general, to attain value also from a speculative point of view on the organization and general economy of living beings on earth.
The classic example of this dependence of animals on plants is that of organic substances of every kind—carbohydrates, fats, proteins, etc.—which, elaborated by plants, ensure animal nutrition. It is not to be thought, however, that animals find in plants only foodstuffs, but very often also stimulating and regulating substances; suffice it to consider the vitamins of every kind, which, though so necessary for the normal course of animal life, are synthesized solely by plants. One may also ask whether a multitude of substances that appear in great number and quantity in the metabolism of plants, and whose significance for the plant organism is often entirely obscure, may not be properly appreciated unless they are considered in the general plan of the economy of living beings on earth. We refer to essences, terpenes, camphors, and above all alkaloids and glucosides, typical products of plant organisms that are of such great importance in the therapy of animals.
As regards man in particular, the interest of plants is even greater when one considers that not only does he find in them food and medicine, but that most of his activities and industries are carried on by utilizing the activity of plants.
Even the thermal, mechanical, electrical, etc., energy that man uses in the functioning of so many of his activities is nothing other than radiant energy from the sun that plants have largely captured during the process of photosynthesis and of which they have determined the formation of immense deposits in the form of various kinds of fossil fuels.
It must also be added that the very energy that man knows how to harness by exploiting waterfalls or, in any case, the movement of liquid masses is largely conditioned by plants, meteorology being profoundly influenced by them through the imposing intensity of their processes of absorption and transpiration.
Equally fascinating, for those interested in the general ordering of life on earth, are the phenomena of interdependence and cooperation among the different groups of plants. A most instructive example of these is found in the carbon cycle.
Green plants are incapable of utilizing the enormous masses of carbon that exist on earth in the form of carbonates, and for their nutrition they use only the carbon dioxide present in the air in the modest proportion of 0.03%.
It has been calculated that chlorophyllian photosynthesis annually fixes and thus removes from the atmosphere about 60 trillion kilograms of carbon dioxide, which means that, if carbon dioxide were not continuously replenished in the air, the supply would be totally consumed in 35 years; at the end of which time the possibility of plant life—and consequently of animal life—would cease.
A certain replenishment of carbon dioxide is ensured to the atmosphere by the respiratory processes that continuously occur in both animals and plants, but processes of fermentation that take place in the soil through the action of plant microorganisms assume far greater importance in this regard. These microorganisms, by incessantly breaking down enormous quantities of organic residues that continuously reach the soil, restore to the atmosphere, in the form of carbon dioxide, the carbon contained in them and thus complete the cycle. Such fermentation processes occur in two stages: first, anaerobic microorganisms intervene, which, though living in the surface layers of the soil, are active only outside contact with atmospheric oxygen. In addition to a certain quantity of carbon dioxide, which is returned to the atmosphere, products of their activity are other diverse organic substances such as alcohol, lactic acid, butyric acid, methane, etc. These compounds still contain carbon in greater or lesser proportion, so that the complete restoration of this element to the air cannot occur until after further and complete breakdown of the products of anaerobic organisms’ activity. This is accomplished by other aerobic plant microorganisms, which take up the products of anaerobic fermentation and, through oxidation processes, further break them down into water and carbon dioxide. Anaerobic and aerobic microorganisms thus carry on an activity that is not only mutually beneficial but indeed necessary. They live, in fact, in strict association, and while anaerobic microorganisms provide aerobic ones with the products of fermentation, necessary for their life, the aerobic ones, avid for the oxygen they need to oxidize completely the organic substances on which they live, withdraw this gas from the environment, rendering it thus suitable for the life of anaerobic organisms.
The life of the plant microorganisms (bacteria and fungi) that teem in the soil reveals one of the many aspects of its extreme importance. Their role depends not only on the fact that, by breaking down the enormous quantity of organic residues that continuously reach the soil and that, like cellulose, are often unusable by higher plants and animals, they prevent the immense energy contained in such residues from being lost. It also depends on the fact that certain bacteria, deriving energy from these fermentation processes, use it to fix atmospheric nitrogen, thus also conditioning the life of all other plant and animal beings.
Even in this case, their supply would quickly run out if there were not bacteria in the soil that, breaking down organic substances of the carbohydrate type which reach the soil in enormous quantities with the dead residues of higher plants, derive the energy that enables them to fix atmospheric nitrogen. In this way, they prepare the nitrogenous materials that will serve the life of other plants and, after these have organized them, the life of animals as well.
Meanwhile, from the breakdown of nitrogenous organic substances by other bacteria, another large quantity of nitrogen returns to the soil in the form of ammonia, which higher plants could use for their nitrogenous nutrition. It has been shown, however, that higher plants are very often unable to use ammonia nitrogen and that, in any case, they greatly improve their nitrogenous nutrition if, instead of ammonia salts, they find more oxidized inorganic nitrogen compounds in the soil, such as the salts of nitric acid. Now, there exists in the soil a complex of bacteria with strictly coordinated activity: some oxidize ammonia to nitrous acid, others take up nitrous acid and oxidize it further to nitric acid. There is an absolute interdependence between these bacteria and those that break down organic substances, which is also why they are difficult to isolate for study.
They live, in fact, in strict association, and in the chain of decomposing bacteria–nitrous bacteria–nitric bacteria, each group provides the material necessary for the next and removes from the previous group the product of its activity, which is toxic to II. From these oxidative processes, the individual groups of such bacteria derive the energy that allows them to organize autotrophically by chemosynthetic means from the carbon dioxide of the air; at the same time, they ensure higher plants a better nitrogenous nutrition.
Similar cooperative phenomena ensure, in nature, the cycle of sulfur.
This is an element that plants cannot do without, since it enters into the composition of protein substances, the main constituents of protoplasm. In protein substances, sulfur is present in the reduced form of sulfhydryl, and it is in sulfhydryl form that it returns to the soil when organic residues, both plant and animal, are broken down.
Sulfhydryl sulfur, however, is not only unusable by higher plants but is actually highly toxic to them; they require soil compounds of sulfur in the most oxidized form, such as the salts of sulfuric acid. It is clear that, little by little, all the sulfate reserves in the soil would be exhausted and transformed into sulfidic compounds, making both plant and animal life impossible. There do exist, however, in the soil specialized bacteria for which sulfhydryl sulfur is not only harmless but even necessary for life. These are the sulfur bacteria, which oxidize hydrogen sulfide to elemental sulfur, then to sulfur dioxide, which is transformed into sulfurous acid and, by oxidation, into sulfuric acid. During these oxidation processes, energy is released that also ensures these bacteria the possibility of autotrophic life and chemosynthetic organization of carbon dioxide from the air, while at the same time, with the sulfur cycle closed, the possibility of life for other plants and animals is made possible.
Examples of such cooperations could be multiplied. Let us recall also those useful cohabitations known as mutualistic symbioses, in which both partners benefit. The best known is certainly lichen symbiosis, resulting from the cohabitation of an alga with a fungus; the result is a kind of new organism capable of living where neither the fungus nor the alga could survive alone. This is, however, a symbiosis whose importance for the general economy of life on earth is quite limited. Far more important are those symbioses known as mycorrhizae, consisting of a particular form of association between higher fungi and the roots of a great many plants.
The importance of these associations is such that very often the life of each symbiont is impossible if they are separated, so much so that the area of distribution on earth of many higher plants is limited by the area of distribution of the fungus, and vice versa.
The relationships between the two symbionts are not entirely clear; there is certainly an exchange of materials whose value is often not merely that of foodstuffs but also of indispensable vitamins. Thus, one type of food may be exchanged for another type of food; a vitamin for another; a food for a vitamin; but it also happens that the two symbionts cooperate in the synthesis of a vitamin necessary to both, of which each is capable of forming only a part, so that the complete synthesis is possible only through the coordination of the activity of the two symbionts. Another important form of cohabitation is that which occurs between certain plants, belonging especially to the legume family, and certain bacteria whose activity results in the fixation of atmospheric nitrogen. This very important process—which, by integrating with the fixation of nitrogen by bacteria living freely in the soil and fermenting carbohydrates, ensures higher plants the conditions for life—is possible for such bacteria only when they live in the tissues of the host. In return, the host is provided with a supply of assimilable nitrogen, the excess of which passes into the soil, improving the living conditions for surrounding plants. It is to this circumstance that legumes owe their reputation as soil-improving plants, and it is for this reason that, since time immemorial, agricultural practice has used green manuring with legumes or introduced a legume crop into the rotation of other crops, achieving a natural fertilization of the soil. Symbioses also occur not infrequently between plants and animals, and it is enough to recall the existence of abundant intestinal flora, or in general of bacteria living in the digestive apparatus of the most diverse animals, which, so to speak, are repaid for the nourishment they provide to their hosts by the benefits they derive from particular activities of these.
Other questions of great interest to the scholar who pursues biological research not as an end in itself include those relating to the perfect correspondence between the external form and the internal anatomical structure of each organ and the various functions it must serve; the modifications that such form and structure undergo in different environments, as an expression of perfect adaptation to particular environmental conditions; and many others easily found even in treatises of a general nature.
HISTORY OF BOTANY — Botany is, so to speak, as old as humanity itself: practical considerations prompted the first observations on plants, and it is easy to imagine that the earliest fruits of such observations consisted in the gradual recognition of plants useful as food, those that were inedible, or even poisonous, and trees whose trunks and wood were best suited as building material or in the manufacture of tools and weapons. Practical needs likewise gave rise to a further type of relationship between man and plants when the first attempts and achievements were made in the cultivation of useful plants, and we have evidence that even before the 5th millennium B.C., in the full Stone Age, wheat and barley were cultivated in Central Europe; that numerous food and other plants, such as the date palm, onion, garlic, barley, sesame, flax, etc., were cultivated in Egypt in the 4th millennium B.C.; and that in 2700 B.C. special ceremonies were performed in China for the sowing of rice, soya, wheat, and millet.
Ideal motives also contributed to expanding early knowledge of plants, especially the cult of divinity or, in any case, religious practices that among many ancient peoples were manifested in tree worship. Aesthetic sense and admiration for flowers and green foliage likewise drew man’s attention to plants, and he soon learned to adorn his altars, sacrificial victims, his home, and even his person with bouquets, garlands, and wreaths of flowers and leaves: the love for the Nymphaea Lotus among the Egyptians and Assyrians, for the daisy among the ancient Babylonians, etc., is well known. Another source of great and ancient interest for man in plants was the treatment of diseases, which led to the knowledge of a quantity of medicinal plants, the identification of their most active parts, and the recognition of the action of their extracts.
Thus a considerable body of knowledge was accumulated; but, at least from a historical point of view, we may say that true scientific botany began only from the period for which we possess written works treating of plants: those of the rhizotomists and pharmacologists, though of limited importance, among whom it will suffice to recall the names of Diocles of Carystus and his contemporary Hippocrates of Cos (460-377).
Opposed to them were the geoponists or georgics, who dealt with the cultivation of plants, among whom we may mention a certain Antrotion and the celebrated Democritus of Abdera (460-380).
The earliest writers who left us studies on the classification and life of plants from a theoretical standpoint are Menestor of Sybaris (c. 450 B.C.), Anaxagoras (497-424), Empedocles (495-436), Hippon of Rhegium (c. 440-420), and Plato himself. A considerable advance in botanical studies was made with the work of Aristotle (384-322), most of which, however, has been lost.
Aristotle regarded biology as a deductive science; he therefore proceeded from the general to the particular and did not attach importance to individual observations. He left us very valuable and original, though entirely theoretical, considerations on the life, organization, and reproduction of plants, as well as on the meaning and functioning of their organs. His pupil Theophrastus (371-286) was the first biologist to adopt the inductive method, proceeding from particular facts to theory, and thus founded the true naturalistic approach. Two of his principal works are to be noted: *Historia plantarum* and *De causis plantarum*.
The first, in nine books, deals with the anatomy, morphology, distribution, and systematics of plants; the second, in six books, treats of plant physiology. It is Theophrastus who is the principal representative of botany throughout antiquity, since his successors were mainly physicians who concerned themselves only with medicinal plants; among these a large number of Alexandrian physicians might be mentioned, but medical botany culminates later in the names of Dioscorides, of the 1st century A.D., and his contemporary Pliny the Elder.
Of the latter, a *Natural History* in 37 books is to be noted, of which Books 12 to 27 are devoted to botany.
Agricultural botany also had numerous adherents in this period, and the works of M. Porcius Cato (234-149), M. Terentius Varro, Virgil, and Columella (c. 60 B.C.) are especially famous.
Little progress was made in botany throughout the Middle Ages; few names, indeed, are to be recalled in these summary historical outlines. First among them is that of St. Basil, Bishop of Caesarea (330-79), for the good observations contained in his homilies on the stages of creation; then that of Isidore, Bishop of Seville (560-636), for his *Origines sive Etymologiae*, which, though often naive, are noteworthy for botany. Also notable for botany in the 10th century are the works of the Arab physicians Avicenna (979-1037) and Ibn al-Baytar (1197-1248). In the 13th century, Albertus Magnus (1193-1280) is to be remembered for his *De vegetabilibus* in seven books, the first five of which are devoted to general botany, the sixth to special botany, and the seventh to economic botany; and mention should also be made of the Franciscan friar Bartholomew the Englishman (1260-1300) and the Dominican monks Thomas of Cantimpré (1204-1270/72) and Vincent of Beauvais (c. 1190-1264).
It was in the Renaissance, with the advent of printing and the establishment of “horti,” that progress was made, aided also by the establishment of botanical gardens and herbariums, and, much later, by the invention of the compound microscope. Until the latter took place, however, and indeed until the early 17th century, the development of botany consisted chiefly in the knowledge and description of an ever-increasing number of plants.
The most fundamental concepts of systematics were, however, still very rudimentary, and the nomenclature itself was irrational and confused, so that the results achieved in this period are more of historical than of scientific value.
Many illustrious names are, however, to be noted, the principal among them being those of Otto Brunfels of Mainz (1490-1534), Hieronymus Bock of Heidelsheim (1498-1554), Leonhart Fuchs of Wemding in Bavaria (1501-1566), Conrad Gesner of Zurich (1516-1565), Rembert Dodoens (Dodonaeus) of Mechelen (1517-1585), Charles de l’Écluse (Carolus Clusius) of Arras (1526-1609), Pier Andrea Mattioli (1521-1577), Luigi Anguillara (1512-1570), Castore Durante of Spoletto (1529-1590), Theophrastus Bombastus von Hohenheim (Paracelsus) of Einsiedeln (1493-1541), Gerolamo Cardano of Pavia (1501-1576), and Gaspard Bauhin of Basel (1560-1624).
The invention of the compound microscope, the rise of the new sciences that this event engendered, and the subsequent advances in chemistry and technology gradually deprived botany of its uniformity and its original character as a purely descriptive science.
The first, entirely incidental anatomical observations are due to the English physicist R. Hooke (1665), who was the first to see, in thin slices of cork and elder pith, what he himself called cells.
The true initiator of plant anatomy was, however, Marcello Malpighi of Crevalcore near Bologna (1628–94), who in his works (*Anatomes Plantarum idea*, presented to the Academy of London on 7 Dec. 1671, and *Anatome Plantarum*, published in 1675) set forth accurate observations on the anatomy and histology of plants.
Contemporary with Malpighi, the Englishman Nehemiah Grew (1628–1711) published in 1671 and 1682 his observations, which, however, were largely based on those of Malpighi, though refined and expanded.
To the Dutchman Leeuwenhoek (1632–1723) are owed, in the same period, important cytological observations.
These early findings, however, long remained without further development, and it was only at the beginning of the 19th century that plant anatomy began its most decisive progress.
In a first period, which extends from the dawn of that century to about 1840, anatomical research was purely descriptive in character. Worthy of mention in this epoch are the researches of the Frenchman Carlo Francesco Brisseau-Mirbel (1776–1854), the Milanese abbot Bonaventura Corti (1729–1813), Cristiano Ludolf Treviranus of Bremen (1812–64), Paolo Moldenhauer of Hamburg (1766–1827), Pierre Jean Turpin of Paris (1725–1840), Theodor Hartig of Dillenburg (1805–80), G. B. Amici of Modena (1786–1863), Franz Julius Ferdinand Meyen of Tilsit (1804–40), Giovanni Giacomo Berardi of Erfurt (1774–1850), Heinrich Friedrich Link of Hildesheim (1767–1850), and Karl Asmus Rudolphi of Stockholm (1771–1832).
In a second period (1840–60), anatomical research was chiefly characterized by the application of the embryological method, which gained prominence under the influence of Goethe’s doctrine of metamorphosis. The founder of plant embryology was the Scotsman Robert Brown of Montrose (1773–1858), to whom, however, the discovery of the cell nucleus is erroneously attributed—this in fact having been made by the Italian Mariano Fontana (1746–98).
Of fundamental importance in this period are the works of Hugo von Mohl of Stuttgart (1805–72), who among other things first recognized the nature of protoplasm and demonstrated that it is the substratum of life; of Matthias Jacob Schleiden of Hamburg (1804–81), who gave the first enunciation of the cell theory; of Karl Wilhelm Nägeli of Kilchberg near Zurich (1817–91), of Franz Unger of Amthof in Styria (1800–70), of Karl Gustav Sanio of Lyck (1832–91), of Johannes von Hanstein of Potsdam (1822–80), of Heinrich Anton de Bary of Frankfurt am Main (1831–88), who first systematically expounded the comparative anatomy of the chromophytes; and finally of Wilhelm Hofmeister of Leipzig (1824–1877), who, on an embryological basis, was able to demonstrate the necessary unity existing among the structures of plants belonging to the different great divisions of the vegetable kingdom.
A third period follows, extending to our own day, dominated by the great problems arising from Darwin’s theory. In it, anatomy developed in numerous directions: through the merit and example of Philippe van Tieghem, anatomy was widely applied to problems of systematics and morphology; the embryological method, closely associated with cytological research, received its greatest impetus from the comparative morphology studies of Eduard Strasburger of Warsaw (1844–1912); by linking anatomical research with studies on functional significance, physiological anatomy was founded, of which the foremost representative was Gottlieb Haberlandt (1854); by adopting the experimental method with Leopold Kny of Breslau (1841–1916), anatomy became experimental morphology; by applying itself to the study of pathology, it became pathological anatomy, especially advanced by Ernst Küster of Breslau (1874, living); it became indispensable to pharmacognosy through the works of Alexander Tschirch of Guben (1856–1939); and it has finally assumed many other aspects that cannot be recalled here.
Plant physiology has a more recent origin, its first fundamental discoveries dating only to the end of the 18th century; the development of this branch of botany merges somewhat with the history of modern chemistry, so much so that many scientists are remembered by both physiologists and chemists.
We may briefly recall the works of Joseph Priestley of Birstall near Leeds in England (1733–1804) and Jan Ingenhousz of Breda in Holland (1730–99), to whom are owed the first observations on the action of green plants on carbon dioxide; these observations later enabled Joseph Pelletier of Paris (1788–1842) and Joseph Bienaimé Caventou of St-Omer (1795–1877) to elucidate the process of chlorophyllian photosynthesis, and R. J. Joachim Dutrochet of Paris (1776–1847) to affirm that respiration is a phenomenon common to all living beings.
Fundamental importance attaches to the studies on plant nutrition by Justus von Liebig of Darmstadt (1803–73). In other chapters of plant physiology, the researches of Thomas Andrew Knight (1759–1838), Thomas Graham of London (1805–69), Stephen Hales of Kent (1677–1761), Julius Sachs of Breslau (1832–97), and Wilhelm Friedrich Philipp Pfeffer of Grabenstein near Kassel (1845–1920), renowned for his studies on osmotic phenomena, are classic.
As for systematics, it is as old as organography and botany itself. Antiquity handed down to us the names of Theophrastus, Dioscorides, and Pliny; and works for the recognition of plants were left to us in less ancient times by P. A. Matthioli, already mentioned, and Ulisse Aldrovandi of Bologna (1522–1605).
The title of pioneers of systematic botany, however, belongs, in addition to the already cited G. Bauhin, to Andrea Cesalpino of Arezzo (1519–1603), Joachim Jung (Jungius) of Lübeck (1587–1657), Robert Morison of Aberdeen (1620–83), John Ray (Raius) of Essex (1628–1705), Augustus Quirinus Bachmann (Rivinius) of Leipzig (1652–90), and Joseph Pitton de Tournefort of Aix in Provence (1656–1708).
The works of these scholars characterize the period known as that of “artificial systems,” in which attempts to arrange plants in a sufficiently rational scheme were based on the choice of arbitrary guiding characters, leading often to serious incongruities and, in any case, to purely arbitrary groupings of plant families and equally arbitrary distributions of these into different groups.
The apex of this period is marked by the studies of Carl Linnaeus of Råshult in southern Sweden (1707–1778). The publication of Linnaeus’s works, the most important of which are *Systema naturae* (1735), *Genera plantarum* (1737), and *Species plantarum* (1753), must be regarded as one of the greatest events in the history of systematics.
Of the merits of this great naturalist, two stand out above all: the refinement and definitive adoption of binomial nomenclature, and the insightful recognition of the importance, even from a strictly systematic standpoint, of the organs of fertilization. It was on their structure that Linnaeus based his system, which for this reason came to be called the “sexual system.”
Linnaeus’s system, however, remained an attempt that, given the limited knowledge of the time, perhaps could not have succeeded. Linnaeus himself had glimpsed the idea of a natural affinity among certain groups of plants; this idea subsequently took ever more concrete form as scientific voyages and paleontological excavations increased knowledge of plants, demonstrating how new findings allowed for a more or less continuous gradation of all living and fossil plants.
Thus the artificial classifications were abandoned and the period of natural methods began; and since it is clear that, on the basis of their natural affinities, plants cannot be ordered except in one way, it is better to say that efforts began to define the natural method.
Among the representatives of this new period the names to be mentioned are those of PIETRO MAGNOL of Montpellier (1638-1715), BERNARDO DE JUSSIEU of Lyons (1699-1776), ANTONIO LORENZO DE JUSSIEU of Lyons (1748-1836), MICHELE ADAMSON of Aix in Provence (1727-1805), AUGUSTO PIRAMO DE CANDOLLE of Geneva (1778-1841), ALFONSO DE CANDOLLE of Paris (1806-93), R. BROWN already cited, ADOLFO TEODORO BROGNIART of Paris (1801-76), STEFANO ENDLICHER of Presburg (1805-49).
This period coincides with the great advances made in the various branches of botany and of science in general; and the enormous ferment that resulted also subsequently took concrete form when evolutionary theories on descent appeared, the chief exponents of which were Darwin and Lamarck.
The task of systematics therefore appears to be that of reconstructing the genealogical tree of all plants down to the identification of the single primitive stock from which the entire vegetable kingdom would have derived its most remote origin.
Among the most notable botanists who illustrated the modern trend in systematics are to be remembered the names of ALESSANDRO BRAUN of Ratisbon (1805-77); of AUGUSTO GUGLIELMO EICHLER of Neukirchen (1839-87), who proposed a classification very close to that now in use; of ADOLFO ENGLER of Sagan (1844-1930); of RICCARDO WETTSTEIN of Vienna (1805-1931); of GIAN PAOLO LOTSY of Dordrecht (1807-1931); of UGO DE VRIES of Haarlem (1848-1935) and of the Japanese B. HAYATA d. in 1934.
It must however be noted that, if the enthusiasm at first aroused by evolutionary theories had suggested the idea of an actual genetic affinity and of a single origin of all plants, indeed of all living things (it was E. Haeckel who was the chief apostle of this monistic theory), the progress of science has subsequently shown the impossibility of referring all living organisms to a single ancestral stock and of arranging the vegetable kingdom in a linear series. Thus it has come to be admitted, within the vegetable kingdom, that there exist several autonomous and independent groups derived from distinct archetypes between which it is impossible to establish any connection; and from a monophyletic concept we have passed to a polyphyletic one. And it must also be said that the affinities between the systematic categories above the species now appear to us more and more as matters of convention, as so many hypotheses whose demonstration cannot be attained.
The history of the vegetable kingdom has thus deepened its mysteries as we have attempted to penetrate them. It is interesting to note that in the latest editions of the *Syllabus der Pflanzenfamilien* by Engler and Diels, in which the ideas of scientists of every country are collected, the vegetable kingdom has been divided into 14 phyla which show no relationship among themselves and are simply listed one after another without this implying, either implicitly or explicitly, any bond of derivation of each phylum from the one preceding II. - See Pl. CXVII.