BOTANY. - Botany, or phytology, is the science of plants. There are three principal aspects under which plants are considered: morphological, physiological, and systematic.
The chapters of morphology, or the study of form, are various: cytology, which deals with the structure of individual cells; histology, or the study of tissues; anatomy, which, by recognizing the distribution of the different types of tissues in the plant, establishes the internal structure of the individual organs; organography, which describes the external form of plants and their organs; finally, the chapters that concern the cytology of reproduction, embryology, etc.
Even more numerous are the chapters of physiology, or the study of functions.
The life of plants unfolds through a continuous introduction of materials that largely have the significance of food. Unlike animals, which cannot nourish themselves except on organic substances, plants typically have the capacity to nourish themselves on mineral substances. Once introduced into the body of the plant, such substances are first of all transformed, by means of an entire series of chemical reactions, into organic compounds; subsequently, and through new successive modifications, they are, to a greater or lesser extent, organized, that is to say transformed into the living substance itself, or protoplasm.
The series of transformations to which the materials introduced into the plant are subjected does not stop at this point, since the various phenomena that accompany life bring about a continuous wearing down of the living substance and, consequently, a continuous breakdown of its constituents, which go on being further transformed with a tendency to assume once again the inorganic state. In any case, numerous compounds appear in living cells, some still organic, others mineral, which, having the value of waste substances, are eliminated. A similar fate is undergone by other materials which, having reached the organic form and even before being organized, whether after a more or less advanced breakdown or even as they are, are likewise eliminated forever or even only temporarily.
The same mineral substances introduced by plants may then not be utilized and may be eliminated without even having undergone the processes of organization. It is therefore an incessant and exceedingly complex exchange of substances with the external environment that takes place during the life of plants and that constitutes the object of study of a great branch of physiology dedicated precisely to material exchange, or metabolism (v.). In it we distinguish an ascending or synthetic phase (anabolism) which, through the processes of assimilation and organization, leads to the formation of compounds with a more or less complex molecule, such as those that participate in the constitution of living matter; and a descending or analytic phase (catabolism) which, by inverse processes, leads to the appearance of waste substances, sometimes with an extremely simple molecule.
Among the processes that form the object of study of distinct chapters of the physiology of material exchange, mention may be made of those concerning the physiology of the intake of water, of its dispersal, of its transport; the physiology of mineral nutrition; the organization of carbon by photosynthetic and chemosynthetic means; 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, an exchange of energy also takes place in plants.
The organization of carbon, in green plants, is made possible by their capacity to utilize the radiant energy of sunlight, and a conspicuous part of the products of this process constitutes, in plants, a reserve of energy. With the breakdown of these compounds, in fact, the same quantity of energy that had been taken from light for their synthesis is released and utilized in the carrying out of a quantity of other reactions. These processes of breakdown, or of dissimilation, proceed in different ways and with or without the intervention of molecular oxygen from outside; thus we have those groups of phenomena that are known by the names of aerobic respiration, intramolecular respiration, and fermentations.
Still other branches of physiology are those that concern growth (the germination of the seed, the ways in which internal and external factors influence growth, the movements of growth and the orientation of plants, the conformation of plants and the factors that determine it; teratology, or the study of abnormal forms, etc.); development, that is to say the ways in which, in the course of its life, the plant acquires new properties that lead it to reproduction and death; the physiology of sexuality and of reproduction; the mechanism of the transmission of hereditary characters, both from the cytological and from the functional point of view; the movements of plants; and ecology, that is to say the study of the relations of plants with the external environment and the modifications, both structural and physiological, that environmental characteristics induce in them, and so on.
Of special botany, the branch perhaps best known to the uninitiated is systematics, or taxonomy, which, alone or almost alone, represented the whole of botany in antiquity and in the Middle Ages. The aim of systematics is the knowledge of all plants and their distribution in a scheme which, while permitting their practical recognition (classification), corresponds to determinate scientific requirements.
The first task of systematics is to establish the categories into which to distribute or group the various plants; the most fundamental of these categories is the species, an entity which, although it was among the first that scientists recognized, the progress of science has made ever more difficult to define and to circumscribe within natural limits, so much so that innumerable discussions are and have been held on the value of this systematic category and on its real existence. Without entering here into particulars, it is impossible to pass over in silence the fact that the importance of these discussions is all the greater in that on their outcome depends whether or not to accept the principle of fixity or of mutability of living forms, whether to accept the creationist connection of individual species or the evolutionist theory, and the very orientation of science with regard to a quantity of problems inherent in the origin of life on earth and which overstep into the philosophical and transcendental field.
Other systematic categories, of an ever more general type, are the genus, the family, the order, the class, the division.
The result of such a work of bringing together and grouping into categories having ever more generic similarities is the creation of a general scheme in which a determinate position is reserved for every form. Naturally, according to the characters chosen for their construction, the value of such schemes will be quite different, and the progress of systematics, from antiquity to today, has consisted precisely in the progressive search for guide-characters such as to permit the construction of a natural scheme, or system, in which, that is, plants are distributed on the basis of their natural affinities.
Scientific problems and philosophical problems interfere here once again, since it is a question of establishing whether the affinity of the different plant forms is such as to admit a monophyletic origin for them, from a single ancestral archetype, or a polyphyletic origin.
The principal characters on which modern systematics is founded are given by the comparative study of the mechanism of reproduction, of the structure and function of the sexual organs, of the embryology of the various forms and of their ontogenetic cycle.
Auxiliary disciplines of systematics, and themselves also part of special botany, are phytopaleontology and phytogeography.
The task of the first is the knowledge of plant forms that lived in other geological eras and are today extinct; the second, on ecological and karyological bases and using geological and climatological data, sets out to account for the floristic composition of the different zones of the earth and of their individual territories.
Another great branch of special botany is, finally, applied botany, whose main chapters are agricultural botany, forest botany, horticultural botany, plant pathology, pharmacognosy, etc.
The interest of so vast and so complex a discipline as botany is evident; like the study of animals, the study of plants surpasses the human aspiration to knowledge as an end in itself, since what is at stake here is the study of life, of its origin, of its manifestations and of its essence. From a certain point of view, moreover, the interest of the study of plant organisms prevails over that of animals themselves, and the reason is that only plants are autotrophic organisms while animals are heterotrophic. Only plants, in other words, are capable of feeding on substances in the mineral state, while animals, which do not have this capacity, are obliged to make use of materials already rendered organic by plants.
All animal life thus appears to us dependent on plant life, and the life on earth of animal organisms, just as they are, is made possible, and so to speak prepared, by the necessarily more ancient existence of plants.
The knowledge of the processes of organization of carbon, nitrogen, sulfur and phosphorus by plants consequently acquires an interest that transcends the purely botanical and even, more generally, biological aspect, to acquire value also from a speculative point of view on the organization and the general economy of living beings on earth.
The classic example of this dependence of animals on plants is that of organic substances of every type, carbohydrates, fats, proteins, etc., which, elaborated by plants, ensure animal nutrition. It is not to be believed, however, that animals find in plants only food, but very often also stimulating and regulating substances; let the example of vitamins of every type suffice, which, so necessary for the normal unfolding of animal life, are nevertheless synthesized by plants alone. And it is also to be asked whether a quantity of substances that appear in great number and in considerable quantity in the metabolism of plants, and whose significance for the plant organism is very often entirely obscure, can be rightly appreciated only by considering it within a general plan of the economy of living beings on earth; we allude to essential oils, terpenes, camphors and, above all, to alkaloids and glucosides, typical products of plant organisms and which have so much importance in the therapy of animal ones.
As regards man in particular, the interest of plants is still greater when one considers that not only does he find in plants food and medicine, but that most of his activities and industries are carried on by availing themselves of the activity of plants.
The very thermal, mechanical, electrical energy, etc., that is utilized by man in the functioning of so many of his activities, is nothing other than radiant energy from the sun which plants have captured in great quantity during the photosynthetic process and of which they have determined the formation of immense deposits in the form of fossil fuels of various types.
It should also be added that the very energy that man knows how to realize 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 one interested in the general ordering of life on earth, are the phenomena of interdependence and cooperation among the different groups of plants. An extremely demonstrative example of them is found in the carbon cycle.
Green plants are incapable of making use of the enormous masses of carbon found on earth in the state of carbonates, and use, for their nutrition, only the carbon dioxide present in the air in the very modest proportion of 0.03%.
It has been calculated that chlorophyllian photosynthesis annually [produces] organic [matter], and therefore removes from the atmosphere, about 60 billion kg of carbon dioxide, and this means that, if carbon dioxide were not again and continuously poured back into the air, the supply of it would be totally consumed in 35 years; at the end of which the possibility of plant life would cease and, consequently, also of animal life.
A certain replenishment of carbon dioxide is assured to the atmosphere by the respiratory processes that continuously take place in animals as in plants, but of far greater importance in this regard are the processes of fermentation that take place in the soil through the action of plant microorganisms which, by incessantly breaking down enormous quantities of organic residues that continuously reach the soil, return to the atmosphere, in the form precisely of carbon dioxide, the carbon contained in them and of which they close the cycle. Such fermentation processes occur in two stages: first anaerobic microorganisms intervene which, although living in the surface layers of the soil, are active only outside contact with the oxygen of the air. Besides a certain quantity of carbon dioxide, which is returned to the atmosphere, products of their activity are other different organic substances such as alcohol, lactic acid, butyric acid, methane, etc. Such compounds still all contain carbon in a more or less large proportion, so that the complete return of this element to the air can occur only after further and complete breakdown of the products of the activity of the anaerobic organisms. This is what happens through the action of other aerobic plant microorganisms which take up the products of anaerobic fermentations and, by processes of oxidation, break them down further down to water and carbon dioxide. Anaerobic and aerobic microorganisms thus carry out an activity that is reciprocally not only useful but even necessary. They live, in fact, strictly associated, and while the anaerobic ones provide the aerobic ones with the products of fermentation, necessary to them for life, the aerobic ones, most avid for oxygen, which they need to oxidize completely the organic substances on which they live, remove this gas from the environment, thus making it suitable for the life of the anaerobic organisms.
The life of the plant microorganisms (bacteria and fungi) with which the soil teems thus reveals one of the numerous aspects of its extreme importance; an importance that depends not only on the fact that, by breaking down the enormous quantity of organic residues that continuously reach the soil and that, as, for example, cellulose, are often unusable for higher plants and for animals, they prevent the immense energy patrimony contained in such residues from being lost, but also on the fact that, from the energy that during these fermentation processes they obtain, certain bacteria make use of it to fix atmospheric nitrogen, thus also conditioning the life of all other plant and animal beings.
While, in fact, the air is for four fifths composed of nitrogen, plants are, in general, incapable of using it and utilize for their nutrition only the few nitrogenous compounds that they can find in the soil.
Even in this case their supply would rapidly be exhausted if in the soil there did not exist bacteria that, by breaking down precisely organic substances of the carbohydrate type and that reach the soil in enormous quantity with the dead residues of higher plants, obtain the energy that makes them capable of fixing atmospheric nitrogen, thus preparing the nitrogenous materials that will serve for the life of the other plants and, after these have realized their organization, for the life also of animals.
From the breakdown of nitrogenous organic substances through the action of other bacteria, another large quantity of nitrogen returns meanwhile to the soil in the form of ammonia, of which the higher plants could make use for their own nitrogenous nutrition. It has however been demonstrated that higher plants are very often incapable of using ammoniacal nitrogen and that, in any case, they greatly improve their nitrogenous nutrition if, rather than ammoniacal salts, they find in the soil more oxidized inorganic nitrogenous compounds, such as the salts of nitric acid. Now, there exists in the soil a complex of bacteria with strictly coordinated activity, some of which oxidize ammonia to nitrous acid, others take up the nitrous acid and oxidize it further to nitric acid. There exists, among these bacteria and among those that break down organic substances, an absolute interdependence that is also the reason for the difficulty of isolating them for study purposes.
They live, in fact, always strictly associated, and in the chain decomposing bacteria-nitrous bacteria-nitric bacteria each group provides the material necessary for the next one and removes from the preceding one the product, toxic to it, of its activity. From these oxidative processes the individual groups of such bacteria obtain the energy that allows them their autotrophic organization by the chemiostatic [chemosynthetic] pathway of the carbon dioxide of the air; at the same time they assure to higher plants a better nitrogenous nutrition.
Analogous phenomena of cooperation assure, in nature, the cycle of sulfur.
It is a matter of an element that plants cannot do without, since it enters into the composition of protein substances, the principal 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, plant as well as animal, are broken down.
Sulfhydryl sulfur, however, is not only not usable by higher plants but is for them even forstrongly toxic; they require finding in the soil sulfur compounds in the form of maximum oxidation, such as the salts of sulfuric acid, but it is evident that, little by little, all the reserves of sulfates in the soil would be exhausted and transformed into sulfhydryl compounds, which would make both plant and animal life impossible. There exist, however, in the soil specialized bacteria for which sulfhydryl sulfur is not only harmless but actually necessary for life. These are the sulfur bacteria, which oxidize the sulfhydryl to elemental sulfur, then to sulfur dioxide, which is transformed into sulfurous acid and, through oxidation, into sulfuric acid. During these oxidation processes, energy is released that also ensures for these bacteria the possibility of autotrophic life and of the chemosynthetic organization of carbon dioxide from the air, while at the same time, the sulfur cycle being closed, the possibility of life for other plants and animals is made possible.
Examples of such cooperations could continue. Let us recall also those associations useful to both partners, which are known by the name of mutualistic symbioses. The best known is certainly the lichen symbiosis, resulting from the coexistence 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. It is, moreover, a symbiosis whose importance for the general economy of life on earth is quite limited. Far more important are those symbioses designated by the name of mycorrhizae, consisting of a particular form of association between the hyphae of higher fungi and the roots of a very great number of 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; an exchange of materials certainly occurs, the value of which is often not only that of food materials but also that of indispensable vitamins. Thus one type of food may be exchanged for another type of food; one vitamin for another; a food for a vitamin; but there is also the case in which the two symbionts cooperate in the synthesis of a vitamin necessary to both, of whose molecule 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. And another important form of coexistence is that which is realized between certain plants, belonging above all to the legume family, and certain bacteria, the fruit of whose activity is the fixation of atmospheric nitrogen. This very important process (which, integrating with the fixation of nitrogen by bacteria that live free in the soil by fermenting carbohydrates, ensures for higher plants the conditions of life) is possible for such bacteria only when they live in the tissues of the host. In exchange, a generous supply of assimilable nitrogen is made available to the host, the excess of which also passes into the soil, improving the possibilities of life for the surrounding plants. It is to this circumstance that legumes owe their fame as soil-improving plants, and it is for this reason that, since time immemorial, agricultural practice has used the green manuring of legumes or introduces a crop of legumes into the rotation of other crops, obtaining a natural fertilization of the soil. Symbioses, moreover, also occur not infrequently between plants and animals, and it suffices to recall the existence of an abundant intestinal flora, or in general, of bacteria that live in the digestive apparatus of the most diverse animals, which are, so to speak, repaid for the nourishment they provide to their hosts by the benefit they derive from particular activities of these.
Other questions of great interest to the scholar for whom biological research is not an end in itself are those relating to the perfect correspondence existing between the external form and the intimate anatomical structure of each organ and the various functions it must serve; to the modifications that such form and such structure undergo in various environments, as an expression of a perfect adaptation to particular environmental conditions; and many others still, easily found even in treatises of a general nature.
HISTORY OF BOTANY
Botany is, one might say, as old as humanity itself: practical reasons gave rise to the first observations on plants, and it is easy to imagine that the first fruits of such observations consisted in the gradual recognition of plants usable as food, of those not edible or even poisonous, and of the trees whose trunks and timber were best suited as building material or in the manufacture of tools and weapons. Practical necessities were likewise the cause of a further type of man's relations with plants when the first cultivations of useful plants were attempted and carried out, 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 plants or plants of other kinds, such as the date palm, the 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 held in China
BOTANY: Diagram of a dicotyledonous plant. — I and II, embryonic stages; III, after germination; G, g, g', buds respectively apical, axillary, cotyledonary; Co cotyledons; I hypocotyl axis; R root; cc central cylinder; Cf root cap. (The embryonic tissues and the zones in the process of elongation are shown in more or less dark hatching); IV and V, sections of the stem and of the root; Co cortex; E endodermis; Pl phloem (or sieve bundles); C cambium; P pericycle; X xylem (or woody bundles); M pith.
for the sowing of rice, soya, wheat and millet. Motives of an ideal order also contributed to broadening the earliest knowledge of plants, above all the worship of the deity or, in any case, the religious practices which among numerous and very ancient peoples manifested themselves in the cult of trees. The aesthetic sense and the admiration for flowers and green foliage contributed in their turn to drawing man's attention to plants, and he soon learned to adorn his altars, the victims of sacrifices, his home and his person with bunches, festoons and garlands 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 motive for man's great and very ancient interest in plants was the treatment of diseases, which led to knowledge of a quantity of medicinal plants, to the identification of their most active part and to the recognition of the action of their extracts.
Thus a body of knowledge certainly remarkable was arrived at; but, at least from the historical point of view, we can say that true scientific botany began only from the era of which writings dealing with plants remain to us: those of the rhizotomists and the drug-sellers, moreover of limited importance, among whom it will suffice to recall the names of Diocles of Carystus and of his contemporary Hippocrates of Cos (460-377).
Opposed to them are the geoponics or georgics, who occupied themselves with the cultivation of plants and among whom we recall a certain Antrotion and the celebrated Democritus of Abdera (460-380).
The most ancient writers who left us studies on the classification and on the life of plants from the theoretical point of view are Menestor of Sybaris (around 450 B.C.); Anaxagoras (497-424), Empedocles (495-436), Hippo of Rhegium (around 440-420) and Plato himself. A conspicuous step forward was made by botanical studies with the work of Aristotle (384-322), the greater part of which, however, was lost.
Aristotle considered biology as a deductive science, descended therefore from the general to the particular and did not give importance to individual observations; he left us very valuable and original considerations, moreover entirely theoretical, on the life, the organization and the reproduction of plants as well as on the meaning and the functioning of their organs. His disciple Theophrastus (371-286) was the first biologist who, for having adopted the inductive method that passes from individual facts to theory, founded the true naturalistic approach. Two principal works of his are to be remembered: Historia plantarum and De causis plantarum.
The first, in 9 books, deals with the anatomy, morphology, distribution and systematics of plants; the second, in 6 books, deals with plant physiology. It is precisely Theophrastus who is the principal representative of botany in all antiquity, since his successors were above all physicians who occupied themselves only with medicinal plants; among these a great number of Alexandrian physicians would be worth remembering, but medical botany culminates later with the names of Dioscorides, of the 1st century A.D., and of his contemporary Pliny the Elder.
Of the latter a Historia naturalis in 37 books is to be remembered, of which those from the 12th to the 27th are devoted to botany.
Agricultural botany too had, in this era, numerous cultivators, and especially famous are the works of M. Porcius Cato (234-149), M. Terentius Varro, Virgil and Columella (around 60 B.C.).
The progress of botany during the whole Middle Ages was not great; few too are the names that, in these summary historical notes, must be remembered. First of all that of St. Basil, bishop of Caesarea (330-79), for the good observations contained in his sermons on the stages of creation; then that of Isidore, bishop of Seville (596-636), for his, in reality often naive, Origines sive Etymologiae. Also noteworthy for botany are, in the 10th century, the works of the Arab physicians Avicenna (979-1037) and Ibn el Beithar (1197-?). In the 13th century Albertus Magnus (1193-1280) is to be remembered for his work De vegetabilibus in 7 books, the first 5 of which are devoted to general botany, the 6th to special botany and the 7th to economic botany; and mention should moreover be made of the Franciscan friar Bartholomew the Englishman (1260-1300) and of the Dominican monks Thomas of Cantimpré (1186-
1270) and Vincent of Beauvais (1194-1264). It is in the Renaissance, and above all after the invention of printing and of the art of reproducing figures, that botany begins its greatest progress, aided also by the institution of "botanical gardens", of herbaria, and, much later, by the invention of the compound microscope. As long, however, as this did not occur, that is until the early 1600s, the development of botany consists above all in the knowledge and description of an ever greater number of plants.
The most fundamental concepts of systematics were nevertheless still very unformed and the nomenclature itself irrational and confused, so that the results achieved in this period have, more than anything else, historical value.
Many illustrious names are nevertheless to be noted, the principal of which are those of Otto Brunfels of Mainz (149-1534), Girolamo Bock of Heiderbach (1498-1554), Leonardo Fuchs of Wemdingen in Bavaria (1501-66), Conrad Gesner of Zurich (1516-65), Rembert Dodoens (Dodonaeus) of Mechelen (1517-88), Charles de l'Écluse (Carolus Clusius) of Arras (1526-1609), Pier Andrea Matthioli of Siena (1501-77), Aluigi Squalerno, called Anguillara from his native place in Latium (1512?-1570), Castore Durante of Spoleto (1529-1590), Theophrastus Bombastus von Hohenheim (Paracelsus) of S. Maria of Einsiedeln (1493-1541), Gerolamo Cardano of Pavia (1501-76) and Gaspare Bauhin of Basel (1550-1694).
The invention of the compound microscope, the rise of the new sciences to which that event gave origin, the subsequent progress of chemistry and of technology gradually made botany lose its uniformity and its primitive character of a purely descriptive science.
The first and entirely incidental anatomical observations are due to the English physicist R. Hooke (1665), who for first saw, in thin sheets of cork and of elder pith, those which 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 London Academy on 7 Dec. 1671, and Anatomes Plantarum, published in 1675) set out accurate observations on the anatomy and histology of plants.
A contemporary of Malpighi, the Englishman Nehemiah Grew (1628-1711) published in 1671 and in 1682 his observations which, however, are based in large part on those of Malpighi, though perfected and enlarged.
To the Dutchman Leeuwenhoek (1632-1723) are due, in the same period, important cytological observations.
These first acquisitions nevertheless remained for a long time without any sequel, and it is only at the beginning of the 19th century that plant anatomy began its most decisive progress.
In a first period, which runs from the dawn of that century until about 1840, anatomical research had a purely descriptive character. To be remembered, in this era, are the researches of the Frenchman Charles François Brisseau-Mirbel (1776-1854), of the Milanese abbot Bonaventura Corti (1729-1813), of Christian Ludolf Treviranus of Bremen (1812-64), of Paul Moldenhauer of Hamburg (1766-1827), of Pierre Jean Turpin of Paris (1725-1840), of Theodor Hartig of Dillenburg (1805-80), of G. B. Amici of Modena (1786-1863), of Franz Julius Ferdinand Meyen of Tilsit (1804-40), of Johann Jakob Bernhardi of Erfurt (1774-1850), of Heinrich Friedrich Link of Hildesheim (1767-1850), of Karl Asmund Rudolphi of Stockholm (1771-1832).
In a second period (1840-60) anatomical research was above all characterized by the application of the embryological method established 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, whereas in reality it was 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, was the first to recognize the nature of protoplasm and demonstrated that it is protoplasm which is the substrate of life; of Matthias Jakob 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 for the first time methodically set out the comparative anatomy of the cormophytes; finally of Wilhelm Hofmeister of Leipzig (1824-1877), who, on embryological grounds, was able to demonstrate the connection of affinity existing between the structure of plants belonging to the different great divisions of the vegetable kingdom.
There follows a third period, which reaches down to our own days, dominated by the great problems that arose in the wake of Darwin's theory. In it, however, anatomy developed in numerous directions: through the merit and after the example of Philippe Léon van Tieghem, anatomy was widely applied to problems of systematics and morphology; the embryological method, widely associated with cytological research, received its greatest impulse from the comparative morphology researches of Eduard Strasburger of Warsaw (1844-1912); by associating anatomical research with that on functional significance, physiological anatomy was founded, whose greatest representative was Gottlieb Haberlandt (1854); by mastering 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, above all applied by Ernst Küster of Breslau (1874, living); it has made itself indispensable to pharmacognosy through the works of Alexander Tschirch of Guben (1856-1939); and it has finally assumed numerous other aspects which cannot be recalled here.
Of more recent origin is plant physiology, whose first fundamental discoveries came only towards the end of the 18th century; the development of this branch of botany is somewhat intertwined with the history of modern chemistry, so much so that numerous scientists are remembered both by physiologists and by chemists.
Let us recall here briefly the works of Joseph Priestley of Birstall near Leeds in England (1733-1804) and of Jan Ingenhousz of Breda in Holland (1730-99), to whom are due the first observations on the action of green plants on carbon dioxide; observations which later allowed Joseph Pelletier of Paris (1788-1842) and Joseph Bienaimé Caventou of St-Omer (1795-1877) to elucidate the process of chlorophyll photosynthesis and R. H. Joachim Dutrochet of Paris (1776-1847) to affirm that respiration is a phenomenon common to all living beings.
Of fundamental importance are the studies on the nutrition of plants by Justus v. Liebig of Darmstadt (1803-73). In other chapters of plant physiology the researches of Thomas Andrew Knight (1759-1838), of Thomas Graham of London (1805-69), of Stephen Hales of Kent (1677-1761), of Julius Sachs of Breslau (1832-97) and of Wilhelm Friedrich Philipp Pfeffer of Grabenstein near Kassel (1845-1920), famous 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 suited to the recognition of plants were left to us, in far less ancient times, by P. A. Matthioli, already mentioned, and Ulisse Aldrovandi of Bologna (1522-1605).
The title of pioneers of systematic botany belongs, however, besides 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 (Rajus) of Essex (1628-1705), Augustus Quirinus Bachmann (Rivinus) 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 the "artificial systems," in which, that is, attempts to arrange plants in a sufficiently rational scheme were based on the choice of arbitrary guiding characters, which often led to serious incongruities and, in any case, to wholly arbitrary juxtapositions between groups of plants and to equally arbitrary distribution of these among the different groups.
The apex of this period is marked by the studies of Carl Linnaeus of Rashult in southern Sweden (1707-1778). The publication of Linnaeus's works, of which the most important are Systema naturae (1735), Genera plantarum (1737) and Species plantarum (1753), must be considered as one of the greatest events in the history of systematics.
Of the merits of this supreme naturalist two are above all to be remembered: the perfecting and definitive adoption of binomial nomenclature, and the happy intuition of the importance that, even from the strictly systematic point of view, must be attributed to the organs of fertilization. It is on their structure that Linnaeus established his system which, for this very reason, was called "sexual."
Linnaeus's attempt nevertheless remained a mere attempt which, given the still limited knowledge of the time, perhaps could not even have succeeded. Moreover, the idea of a natural affinity between certain groups of plants had already flashed upon Linnaeus himself; this idea gradually took on an ever more concrete form as scientific voyages and paleontological excavations secured knowledge of an ever greater number of plants, demonstrating how the new knowledge permitted a more or less continuous seriation of all living and fossil plants.
Thus 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 can be ordered in only one way, it is better to say that the efforts to define the natural method began.
Among the representatives of this new period, mention should be made of the names of Pietro Magnol of Montpellier (1638-1715), Bernard de Jussieu of Lyon (1699-1776), Antoine Laurent de Jussieu of Lyon (1748-1836), Michel Adanson of Aix in Provence (1727-1805), Augustin Pyramus de Candolle of Geneva (1778-1841), Alphonse de Candolle of Paris (1806-93), R. Brown already mentioned, Adolphe Théodore Brongniart of Paris (1801-76), Stephan Endlicher of Pressburg (1805-49).
In this period the great advances made in the various branches of botany and of science in general coincide; and the enormous ferment that resulted gradually took concrete form when the evolutionist theories on descent took shape, whose major exponents were Darwin and Lamarck.
The task of systematics thus appears to be that of reconstructing the genealogical tree of all plants to the point of identifying the single primitive stock from which the entire plant kingdom would have drawn its most remote origin.
Among the most distinguished botanists who illustrated the modern direction of systematics, mention should be made of the names of Alexander Braun of Regensburg (1805-77); of August Wilhelm Eichler of Neukirchen (1839-87), who proposed a classification very close to that currently used; of Adolf Engler of Sagan (1844-1930); of Richard Wettstein of Vienna (1865-1931); of Jan Paulus Lotsy of Dordrecht (1867-1931); of Hugo de Vries of Haarlem (1848-1935) and of the Japanese B. Hayata, d. 1934.
It should be noted, however, that if the enthusiasm initially aroused by the evolutionist theories had suggested the idea of an actual genetic affinity and of a single origin of all plants, indeed of all living beings (E. Haeckel was the greatest apostle of this monistic theory), the progress of science subsequently demonstrated the impossibility of referring all living organisms to a single ancestral stock and of constituting the plant kingdom into a linear series. Thus it came to be admitted, within the plant kingdom, that there exist several autonomous and independent groups derived from distinct archetypes among which it is impossible to establish a connection; and from a monophyletic concept, we have passed to a polyphyletic concept. And it must also be said that the affinities between systematic categories higher than the species appear to us today as increasingly conventional in value, like so many hypotheses whose demonstration cannot be achieved.
The history of the plant kingdom has thus accumulated its mysteries as attempts have been made to penetrate them. It is interesting to note how in the latest editions of the Syllabus der Pflanzenfamilien of Engler and Diels, gathering the ideas of scientists from every country, the plant kingdom has been divided into 14 stocks that show no relationship among themselves and that are simply listed one after another without this implying, either implicitly or explicitly, a link of derivation of each stock from the one preceding it. - See Pl. CXVII.
