Pfeffer, Wilhelm Friedrich Philipp

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(b. Grebenstein, near Kassel, Germany, 9 March 1845; d. Leipzig, Germany, 31 January 1920)

botany, chemistry.

Pfeffer was the son of wilhelm Wilhelm, an apothecary in Grebenstein, and Luise Theobald, whose family was associated with the clergy. His parents intended him to be the third successor to the apothecary shop founded by his great-grandfather; and even after several years of university study, Pfeffer still planned to enter the profession of pharmacy. He thus made sure of a strong background in chemistry, physics, and botany; and his theoretical studies and practical experience in preparation for such a career provided him with broad insight as well as techniques that would become useful in fine experimentation when he turned his full attention to botany, and especially to plant physiology.

Pfeffer attended the grammar school in Grebenstein until he was twelve; then, after additional private instruction, he entered the electoral Gymnasium near Kassel. Three years later (before he had completed his Gymnasium studies) his father took him into the apothecary shop as an apprentice. Pfelfer’ father, a man of a man of braod scientific interests, had a large herbarium and had gathered extensive collections in many fields of the natural sciences; he also wrote and corresponded with scientists in Germany and abroad. He supplemented his son’s education in manyways and imbued him with his own enthusiasm for the study of nature. Pfeffer received an early introduction to botany by accompanying his father on expeditions into the nearby countryside, and at the age of six he was pressing flowers and collecting speciamens for several of his own collections. The scope of Pfeffer’ explorations was considerably widened when, at the age of twelve, he began to make excursions into the high Alps with his uncle Gottfried Theobald, whose geological and botanical trips kindled the boy’s enthusiasms still further while also developing his ability as an alpinist. Pfeffer was fearless about searching in difficult locations for certain mosses and rare plant specimens, and he became one of the earliest to climb the Matterhorn. After his marriage (1884) to Henrika Volk, Pfeffer avoided such hazardous mountaineering, although visiting the Alps was always his favorite vacation.

As an apprentice to his father, Pfeffer prepared plants and herbs and ground ingredients, made up chemicals and medicinal preparations, and was responsible for various analyses. He also maintained the shop, which dispensed not only pharmaceutical chemicals but sold homemade candies, cleansers, and even shoe polish prepared on the premises. Pfeffer also used his father’s microscope to examine the fine structure of various specimens of seeds, fibers, and starches; these observations were aided by texts on the microscope and Mohl’s Grundzuge der anatomie und Physiologie der vegetablischen Zelle. After passing the examination for apothecary’s assistant, Pfeffer entered the University of Gottingen to study chemistry and prepare for a career in pharmacy.

At Göttingen Pfeffer attended lectures in physics, chemistry, zoology, and botany; and although his atypical preparation for the university had left deficiencies which he now strove to remedy, he was able to begin a dissertation in chemistry shortly after his matriculation at the age of eighteen. He submitted this work, “Uber einige Derivative des Glyzerins und dessen Überführung in Allylen,” and received his doctorate in chemistry and botany in early February 1865, having spent barlely four semesters at Göttingen.

In the summer of the same year, at Marburg, Pfeffer continued his pharmaceutical studies and for the time being set aside consideration of an academic career, thus following his father’s whishes. He then received an assistantship at an apothecary in Augsburg and later in Chur, wher his uncle still taught in the canton school. Pfeffer resumed alpine climbing with his uncle and gathered the mosses that were to be the subjects of his first papers. He subsequently returned to (lie llrmcrsily of Marlmig and in December 1869 passed the examination passed the examination qualifying him for the profession of apothecary, as his father had desired. He now became more certain, however, of his preference for an academic career in botany. Encouraged by the botanist Albert wignad, Pfeffer studied the development of blosssoms; he then went to Berlin at the end of the next summer and obtained a much sought-after place in Pringsheim’s private laboratory, where the activity centered about investigations of the developmental history of plants. Here Pfeffer began his studies of the germination of Selaginella. He continued this work in Wurzburg under the plant physiologist Julius von Sachs, who encouraged Pfeffer to direct his researches to problems in plant physiology. He thus studied the effects of light from different parts of the spectrum on the decomposition of carbon dioxide in plants and analyzed some of the effects of external stimuli on the growth of plants. The chemistry and physics he had previously studied were already of great help to Pfeffer, and he presented some of this work for his habilitation at Marburg.

In March 1871 Pfeffer was appointed Privatdozent at Marburg, wher he investigated protein metabolism in plants and was especially concerned with the formation and diffusion of asparagine. He also began extensive researches, which continued for many yeras, on irritability in plants, studying movements due to irritability in the “sensitive plant,” Mimosa pudica, and the staminal filaments of Cynareae. From his observations of irritability phenomena and his understanding of their broad implications, Pfeffer undertook his classic investigations of osmosis, with a view toward explaining the basic causes and mechanisms of such manifestations. Pfeffer’s osmotic investigations were first pursued at Marburg and continued at the University of Bonn, where, in 1873, he was appointed professor extraordinarius of pharmacy and botany. He made the first direct measurements of osmotic pressures in plants during these studies, which, published in his Osmotische Untersuchungen (Leipzig, 1877), were to provide van’t Hoff with the values for his calculations. Thus Pfeffer’s work was invaluable in the development of the theory of solution, itself a landmark in the history of physical chemistry.

At Bonn, where he was alos custodian of the Botanical Institute, Pfeffer’s various researches included studies of the periodic movements of leaf organs. In 1877 he was appointed professor of botany at the University of Basel, but in the fall of 1878 he accepted a post at the University of Tubingen. During nine years here he investigated plant irritability and respiration. His work on chemotais, which evolved from this period, demonstrated the attraction of certain specific substances for the small, free-swimming organisms he was studying: it appeared that malic acid drew the spermatozoids of ferns and Selaginella to the archegonium, for they were as readily drawn to the capillary tubes that Pfeffer filled with this solution. In certain mosses Pfeffer discovered that a similar stimulus was exerted by a cane-sugar solution. He also found chemotropism in bacteria, flagellates, and various other organisms.

In 1881 Pfeffer published his comprehensive Pflanzenphysiologie which became a well-known reference work. It presented not only a mine of information buy also a view of Pfeffer’s aims and philosophy as a physiologist studying fundamental life processes with plants as his subjects. His investigations probed all implications indefatigably, and he was ingenious at devising apparatus for acute measurements and various laboratory experiments. Pfeffer followed specific phenomena in his search for ultimate causes. He was convinced that changes in energy underlay the processes of plant life and that the phenomena of life, if penetrated, would be understood“ as the natural consquences of given conditions,” Yet he stressed the complexities of life processes: Within each cell there were constellations of still finer organizations and chains of interrelated reactions, and within each organ there were intricately correlated relationships. In the living organism there was a cooperation and self-regulation of the whole; following disturbances, this relationship tended to restore the previous equilibrium or establish a new state.

Students from both Germany and abroad entered Pfeffer’s botanical laboratory at Tubingen, where they found a unique combination in his personal stimulus to their researaches and the chance to work with a teacher whose knowledge of physics and chemistry had enabled him to pursue a range of microchemical and other investigations and to construct fine physical apparatus. Pfeffer was unmatched in setting up instrumentation to measure plant movements, growth, and osmotic pressure, and to pursue other observations toward the solution of complex problems of plant physiology. He had a penchant for theorizing, for exploring the range of possibilities, and for exactitude. His student’s papers and some of his own appeared in the Untersuchungen aus dem botanischen Institut zu Tübingen (1881ȃ1888).

In 1887 Pfeffer was appointed professor of botany at the University of Leipzig, where he was again active in teaching and busy with administrative duties and was the director of the Botanical Institute. His responsibilities were increased in 1895 when, following the death of Pringsheim, he became coeditor with Eduard Strasburger of the Jahrubuch fur wissenschaftliche Botanik.

Pfeffer was a member of many leading societies, both German and foreign; and his honors included degrees from the universities of Halle, Konigsberg, and Oslo. Cambridge University awarded him the honorary degree of doctor in science in 1898.

At Leipzig the number of Pfeffer’s students grew; they came from many countries, and many were from the United States. A stimulating teacher in the laboratory, he enlivened his lectures with demonstrations and made use of projection apparatus. In a container for the purpose, students placed slips with questions he would answer at botanical club meetings, and surreptitiously Pfeffer added challenging questions of his own. In 1915, at the age of seventy, a Festschrift of the Jahrbucher fur wissenschaftliche Botanik was dedicated to Pfeffer. (Among his former students named in the volume were Carl Correns and Wilhelm Johannsen). In the same year a special issue of Naturwissenschaften commemorated pfeffer’s scientific contributions.

The last years of Pfeffer’s life, however, were deeply troubled and unhappy; He had become increasingly affected by feelings of depression; the brutality of the war haunted him, and he was apprehensive about the political and social changes he witnessed in Germany. His only son was killed less than two months before the armistice.

Many of Pfeffer’s investigations were basic to plant physiology. His work on the role of asparagine was controversial but nevertheless an advance in the study of plant metabolism when viewed in a historical context. He made extensive contributions to the study of irritability in plants by investigating the movements of leaves, the opening and closing of flowers, the influences of variations of light and of temperature, the effects of tactile stimuli, and the physiology of transmission in irritability phenomena. He also studied the sleep movements of plants. Using aniline dyes, he pioneered the method of viatal staining and followed the assimilation and accumulation of various dyes within the living cell.

Abbé Nollet, in 1748, was the first to explain osmosis; and as Pfeffer noted, the phenomenon had been“rediscovered” several times. Moritz Trauble had even constructed semipermeable precipitation membranes and used them in studying the cell. While searching for the causes of the extremely high osmotic pressures he had observed in plants, Pfeffer improved upon Traube’s membranes. After trying methods that similarly produced membranes that were too freagile and burst under pressure, Pfeffer devised his Pfeffer Zelle, his“pepper pots.” Using unglazed, porous porcelain cells, he precipitated membrances of copper ferrocyanide within them. Thightly supported by the walls of the cells, they withstood increased pressures; walls and Pfeffer was able to make direct measurements of solutions of various sbstances at different concentrations and temperatures. Pfeffer considered this cell a model of the plant cell, or in his terms, the protoplast with its surrounding membranes. His results showed proportionate relationships between the concentrations of the solutions in the cells and the concentrations of the solutions in the cells and the osmotic pressures, and temperature likewise proved to be directly related to osmotic pressure.

Pfeffer, then teaching at Bonn, communicated his findings to the physicist Clausius. The values for the pressures within a plant cell seemed inordinately high at first, and Pfeffer later recalled that Clausius had thought that such pressures must be impossible and was convinced of their accuracy only when Pfeffer gave him further proof. Pfeffer acknowledged, hoever, that Clausius did not examine the question closely at the time.

Some time afterward, at Amsterdam, the botanist De Vries, who was engaged in researches related to osmotic pressures, met van’t Hoff and told him of the values for osmotic pressures that Pfeffer had published in Osmotische Untersuchungen. Van’t Hoff then referred to Pfeffer’s work and drew his braod analogies between osmotic presseures and gas pressures. Thus Pfeffer’s determinations were the values on which van’t Hoff based his theoretical considerations. In his classic paper of 1887 van’t Hoff outlined the experimental method that pfeffer had used in obtaining his determinations. Pfeffer’s technical achievement in making these measurements proved difficult to match.

Pfeffer suggested in Osmotische Untersuchungen that the“threads” he had permitted to fall might be a point of departure for the physicist; later he described his work to Clausius. He recalled,“I repeatedly expressed in conversations with him that some kind of conection had to exist between the osmotic effect on one hand and the size and number of the molecules on the other hand” (E. Cohen, p. 119). Pfeffer was therefore aware of the wider implications of his measurements, even though he never pursued them. Nevertheless, the development of the theory of solution has assured Pfeffer an enduring role in the history of physical chemistry. He was one of the triumvirate who guided German botany in their time; the obituary in Nature stated,“With his death the three outstanding figures of the older German botany—Sachs, strasburger, and Pfeffer—have all passed away."


I. Original Works. Pfeffer’s major works are Osmotische Untersuchungen. Studien zur Zellmechanik (Leipzig, 1877) and Pflanzenphysiologie. Ein Handbuch des Stoffwechsels und Kraftwechsels in der Pflanze, 2 vols. (Leipzig, 1881; 2nd ed., 1897-1904), with English trans. by A. J. Ewart as The Physiology of Plants, a Treatise Upon the Metabolism and Sources of Energy in Plants, 3 vols. (Oxford, 1900-1906). A complete bibliography of 100 titles is given in Fitting (see below)

II. Secondary Literature. A biographical sketch by G. Haherlandt,“Wilhelm Pfeffer,” in Naturwissenschaften, 3 (1915), 115-118, is followed by contributions describing various aspects of Pfeffer’s work: Ernst Cohen,“Wilhelm Pfeffer und die physikalische Chemie,” pp. 118-120; Friedrich Czapek,“Die Bedeutung von W. Pfeffer’s physical ischen Forschungen fur die Pflanzenphysiologice,” pp. 120-124; L. Jost,“Die Bedeutung Wilhelm Pfeffers fur die pflanzenphysiologische Technik und Methodik,” pp. 129-131 H. Kniep,“Wilhelm Pfeffer’s Bedeutung fur die Reizphysiologie,” pp. 124-129.

See also Albert Charles Chibnall, Protein Metabolism in Plants (New Haven-London-Oxford, 1939), 6-34, 37, 42-45, 65, 122, 170-171, for Pfeffer’s views on asparagine and his work on protein metabolism in plants; and Harry Clay Jones, trans. and ed., The Modern Theory of Solution. Memoirs by Pfeffer, van’t Hoff, Arrhenius and Raoutlt (New York-London, 1899), pp. v-vi, 3-10, 14-16, with excerpts from Osmotische Untersuchungen and from van’t Hoff’s paper and its reference to Pfeffer’s determinations of osmotic pressure.

For biographical material see Frank M. Andrews,“Wilhelm Pfeffer,” in Plant Physiology, 4 (1929), 285-288; Hans Fitting, “Wilhelm Friedrich Philipp Pfeffer,” in Deutsches Biographisches Jahrbuch, II (1917-1920), 578-582, 750-751, and“Wilhelm Pfeffer,” in Berichte der Deutschen botanischen Gesellschaft, 38 (1920), 30-63, with a comprehensive bibliography; Wilhelm Ostwald,“Wilhelm Pfeffer,” in Chemiker-Zeitung, 44 (1920), 145; G. J. P. [George James Peirce],“Wilhelm Pfeffer,” in Science, n.s. 51 (1920), 291-292; Hans and Ernst G. Pringsheim,“Wilhelm Pfeffer,” in Berichte der Deutschen chemischen Gesellschaft, 53A (1920), 36–39; V. H. R., “Prof. Wilhelm Pfeffer, For. Mem. R. S.,” in Nature 105 (1920), 302; and Wilhelm Ruhland,“Wilhelm Pfeffer,” in Berichte über die Verhandlungen der Sächsischen Akademie der Wissenschafen zu Leipzig. Math.-Phys. Kl., 75 (1923), 107–124.

Gloria Robinson

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