It was with pleasure that I followed the suggestion of Dr.Heinz Degen to write about the life and work of Wilhelm Pfeffer for the series “Grosse Naturforscher.” This was not done to rescue Pfeffer from oblivion; he has not been forgotten. In fact, he has been quoted more frequently in recent times than in the first decades after his death. This occurred not in reference to minor questions of plant physiology, but rather in reference to major questions of general biology.

After my second reading of Pfeffer’s works — some forty to fifty years after my first reading — I realized that...

Wilhelm Pfeffer is known as a botanist; he was anOrdinarius[full professor] of Botany at universities in Basel, in Tübingen, and in Leipzig. This would not have come about, had it not been for the support of farsighted men who knew how to evaluate Pfeffer’s talent. He had not obtained the Arbitur certificate [matriculation from high school]. In spite of this fact, he was admitted to university. Even then, it would have seemed more appropriate for him to have become a pharmacist or a chemist, certainly not a botanist. By training he was a pharmacist. After four semesters of...

“The human mind is as incapable of comprehending the ultimate meaning of things as it is incapable of comprehending infinity. Newton was absolutely right when he said that he who looks for the ultimate meaning of things, thereby reveals that he is not a man of science” (Pfeffer, 1904, p.4).

Pfeffer was indeed a man of science. One might be tempted to say that he was a man who was interested only in natural science; yet, he did not minimize the importance of other fields. There have been many great scientists who turned to fine arts in their leisure hours,...

With his many talents, Pfeffer could have become not only a botanist or a zoologist, but just as readily a physicist, a chemist or an engineer. He became a botanist thanks to certain influences in his youth.

Pfeffer was born on March 9, 1845 in Grebenstein near Kassel; more specifically, he was born in the pharmacy his father had taken over from the grandfather, and the grandfather from the great-grandfather (fig. 1). He had a private tutor from the age of six to the age of twelve. He then attended the “Kurfürstliche Gymnasium” in Kassel for three years. At age...

Osmosis is diffusion in a solution in the presence of a semi-permeable membrane. Semi-permeable membranes allow water to pass through with relative ease, while substances dissolved in the water either do not pass or pass only poorly. Dutrochet, a plant physiologist, discovered the significance of osmosis, and in 1828, built the first endosmometer (fig. 6).¹⁹However, it was Pfeffer who eventually discovered the very high pressures associated with osmosis.

Pfeffer’s osmotic investigations are an outstanding example of successful scientific research. Experimental skill, combined with logical thinking and planning, led to results of major importance.

The osmotic investigations had their start...

Many of Pfeffer’s contemporaries did not understand the objectives for hisOsmotische Untersuchungen [Osmotic Investigations]and his reasons for postulating a plasma membrane. He was thought of as a scientist belonging to a large group that considered the Traube cell as a model for a living cell. It was believed he had gone too far in comparing the plasma membrane to the lifeless precipitation membrane. The polemic went as far as to say, “A membrane that is not visible is not a membrane.”²³On this subject, Pfeffer wrote:

My concern with the question of the membrane as a separate part...

Pfeffer’s point of view can best be expressed with the above heading. Many people were shocked when in 1961, the Nobel Prize laureates J. Monod and F. Jacob put forward the axiom that everything that is found to be true for (the bacterium)Escherichiamust also be true for elephants. But in fact this statement is only an extension of Pfeffer’s clearly expressed opinion that all physiological achievements of higher organisms depend on cell functions already present in single-celled organisms. The only difference is that a higher organism achieves a greater degree of differentiation and the specialization of distinct organs...

If the study of the attraction of bacteria by oxygen is thought of as chemotaxis, then Theodor Engelmann is its discoverer. Chemotaxis in a broader context means the attracting or repelling effect on motile single-celled organisms by various substances which are in solution in the substratum. Chemotaxis in this sense was discovered simultaneously and independently by E. Stahl and W.Pfeffer.³⁰

In 1884, and again in 1888, Pfeffer reported on the chemotaxis of the spermatozoa of ferns and mosses and on the chemotaxis of bacteria and flagellata.³⁰The method used in the experiments was simple. The substance to be examined was...

Today, the technical terms relay and relay-triggering are commonly understood. Biologists know that in physiology a process of stimulation simply means a process of triggering. In the previous century this was not yet a common concept.

Originally, the idea of a “stimulus” was closely related to psychic experiences of humans; the concept was eventually transferred to animals and then to plants. This led some authors to speak of psychic forces in the plant. They even cited Weber’s law to support their idea because the term “feeling” was used in the original definition of the law.

Other authors rejected the whole...

Since the development of cybernetics, feedback has become a widely accepted concept in modern biology. It is a term which has been adopted from engineering, as were many other terms and concepts of bio-cybernetics. The principle of feedback was noted by some earlier biologists, but it was most clearly formulated by the famous French physiologist Claude Bernard.

Pfeffer stressed the great significance of the feedback principle on many occasions. He wrote:

The correlations and the other phenomena dealt with here are. . . only special cases of the greatly diversified regulatory processes that permeate and direct the whole mechanism of...

It has already been noted that Pfeffer showed great talent and skill in performing his experiments. He developed many methods for these experiments, and he constructed many types of apparatuses which eventually were to be used throughout the world. If one were to list all the methods and experiments developed by Pfeffer and his students, it would result in a reference list of most of the multitude of experiments they undertook. Two examples will be given to illustrate how Pfeffer used the concepts of activation, regulation and feedback in developing his technological methods for the study of physiology, in the...

As noted on page ...., Pfeffer started from the premise that the law of the conservation of energy was generally valid for plant physiology. He and several other physiologists were firmly convinced of the correctness of this premise. The experimental proof was eventually supplied by Z. Rubner in 1894 — two years after Pfeffer’s “Studium zur Energetik der Pflanzen” — using experiments in animal physiology.⁴⁷Pfeffer had firmly rejected any idea that an organism may have special types of energy; he also affirmed that an organism has only those kinds of energy that are known for the inanimate world.⁴⁸

Following the experiments...

“Leaf Movements: Rosetta Stone of Plant Behavior?” This is the title of a paper by R.L. Satter and A.W. Galston published in 1973 in the field of plant physiology.⁵⁰The title is very appropriate since the understanding of leaf movements is of such great significance to the understanding of plant physiology.

The diurnal rhythm of leaf movements was already recognized in the days of Alexander the Great. Androsthenes was on a campaign with Alexander when he observed these movements in some varieties ofPapilionaceae.For the past 200 or more years there have been many reports on these kinds of...

In 1921, Karl von Goebel, the great botanist and expert in morphology wrote, “It is alarming to see how stimulus physiologists are obstinate in studying completely irrelevant details.” There is no doubt that in all fields of biological research, needless time has often been spent on details. If no new ideas are generated, such research may easily deteriorate to the level of an amateur’s collection of butterflies or stamps. The examination of details is only of value if it serves as a lever to penetrate deeper into universal laws. It is evident that Pfeffer used details as such a lever...

The following sentence appears in Wöhler’s evaluation of Pfeffer’s doctoral thesis: “With regard to style, there are many flaws.” While the faculty disregarded these flaws, they should not be simply attributed to the missing years of high school education. It is still an effort to work through Pfeffer’s later publications. His latest work on the periodicity of leaf movements consisted of 150 pages. Today, the standards of most scientific journals would require that this should be compressed to about twenty pages. Almost every sentence in Pfeffer’s works reflects the complexity of biological phenomena and the resulting complexity of arguments and...

In 1840, Purkinje opened one of the first German institutes for physiology in Breslau. Before that, he had been conducting experiments in his own home. Purkinje did not pursue individual problems in a consequential manner; however, he was a successful observer and experimenter in several areas of anatomy and physiology, and he showed great ingenuity in the development of equipment. He and Johannes Müller are considered to be the founders of experimental physiology in Germany. The path from Purkinje leads via Sachs to Pfeffer. The young Julius Sachs used to play with Purkinje’s children in the garden of Purkinje’s house...

Pfeffer’s fame and success and the work of his students led to a decreased interest in plant morphology. As could be expected, many botanists resented this. Von Goebel wrote, “As of late, faculties do not want any part of thePiperaceas(pepper plants) and their one-sided outlook. Even so, they will all get ahead; a large number of professorships in botany must be filled.”⁶⁸However, not every morphologist was a von Goebel, and on the whole, the career successes of thePiperaceasgreatly advanced the study of modern biology. In Germany, systematic botany missed making a connection with genetics. By...

Pfeffer’s contemporaries felt that they could not measure up to him. Even Haberlandt, as outstanding a figure as he was, wrote that he did not feel at ease in Pfeffer’s presence. “Later I saw him repeatedly, but in the presence of this genius and this very critical scientist, I always felt intimidated as if exposed to a blast of ice-cold wind.”⁷³

In the case of personalities such as Pfeffer, there arises the question of heritage, both from the point of view of biological descent and of family tradition. There were pharmacists, clergymen and “scribes” among Pfeffer’s ancestors. This was typical...

Many great scientists succeeded by isolating themselves in their laboratory and by letting others take care of teaching and administrative duties. Pfeffer attended to all these duties in a most conscientious manner. At his funeral service, the representative for the faculty had this to say:

Pfeffer’s great spirit, his clear intellect, his critical sense, all worked to the benefit of the scientific community to which he belonged — the University and the closer circle of the Faculty of Philosophy. Just as he devoted his life to scientific work, he devoted much effort in the service of the community. In meetings, his...

Pfeffer’s accomplishments were given recognition at an early stage. Honours were bestowed on him by German kingdoms and many foreign countries. He was given many medals and decorations, and he was made an honorary member of most academies of sciences and of many scientific societies. Amongst the medals he received was the highest decoration the German Emperor could award, the PrussianPour le Merit[for Sciences and Arts]. A coworker, H. Fitting, relates how Pfeffer felt about these honours: “He was very pleased in a modest but humanly healthy way. It satisfied the ambition that — as he once said —is...

The research performed in Pfeffer’s laboratory did not only give a strong incentive to pure scientific research but also to investigations which led to many applications in medicine (osmosis, Theory of Solutions), agriculture, and horticulture. Many have asked, and some still ask, what purpose there is in “playing” with stamens, with trembling leaves, with bending grass shoots, with “frolicking bacteria” (Pfeffer’s expression) and with porous pots. The doubters can put their minds at ease. The benefits which resulted from this kind of “playing” far outweighed the financial costs.

This does not mean that funding should be made available to all...

In 1893, Pfeffer spoke to a meeting of the Society of German Naturalists and Physicians on the sensitivity of plants. He had this to say about the quest for new knowledge in sciences:

Similar to all natural sciences, the research aimed at unlocking the riddles of the workings of life offers an inexhaustible field of activity. If the researcher brilliantly succeeds in bringing light to a previously dark area of science, he will find that in looking out from this newly secured beach his eye is directed to other unknown regions which call on him to embark on a new...