(b. Walldürn, Baden, Germany, 9 May 1892; d. Tübingen, Federal Republic of Germany, 30 June 1980)
Walter Zimmermann, the son of Emil Zimmermann, a lawyer, and of his wife, Maria Welte, attended the classical gymnasium in Karlsruhe and studied science at the Karlsruhe Technical University as well as at the universities of Berlin and Freiburg. At the latter, studying under Friedrich Oltmann, he received the doctorate in natural sciences (1921). From 1919 to 1925 Zimmermann was an assistant at the Freiburg Botanical Institute. In 1925 he qualified as a lecturer at Tübingen, where he was appointed extraordinary professor in 1930, and full professor and professor emeritus in 1960. He fought as a front-line soldier in both world wars. In 1921 he married Anna Schleiermacher; they had two daughters and a son. Anna died in 1950, and in 1960 Zimmermann married Karin Krause.
Zimmermann’s scientific life’s work was in three main fields: algae, kinetic physiology, and phylogeny (evolution). His first scientific publications were on algae. In his dissertation on Volvox he clarified important points in cytology and the history of evolution. He discovered several new taxa, one of which was the genus Oltmannsiella (the link between Volvocales and Ulotrichales), and studied the polarity of various marine algae.
Zimmermann began his studies of plants’ kinetic physiology in Freiburg and continued them in Tübingen. He investigated a very complex phenomenon, plagiotropism, which occurs in horizontally growing shoots and offshoots, and proved that it has three components: epinasty, negative geotropism, and positive geotropism. Zimmermann also strove to analyze the movement of blossoms. In 1927 he wrote a critical summary of the knowledge of georeactions.
The majority of Zimmermann’s scientific publications, which established his high standing outside Germany, concern plant phylogeny. The first was Die Phylogenie der Pflanzen (1930), in which he describes the course of plant evolution on a paleobotanical basis and discusses the factors of development. The second, completely revised edition of Phylogenie (1959) is a standard work that has no equal in international literature. Zimmermann based his work on fossil plants and treated various problems of evolution in numerous publications. He strove especially to clarify the methodological fundamentals of phylogeny (1931, 1967). He elaborated on the differences between idealistic and phylogenetic morphology, explained the epistemological and methodological foundation, and showed the meaning of “phylogenetic tree” as well as how to construct it. Zimmermann also dedicated (1953) an extensive work to the history of the concept of evolution as well as to research on evolution. He chose several problems from the seemingly inexhaustible material of plant phylogeny proper: the phylogeny of trees, of leaf arrangements, of steles, of the Ophioglossum leaf, of sporophylls, of blossoms, and of inflorescences. He also discussed the phylogeny of individual groups within the plant kingdom, such as bryophytes, pteridophytes, and psilophytes. The last group led Zimmermann to develop his “telome theory”, that the oldest cormophytes are built from undifferentiated single organs (telomes). The great morphological diversity of cormophytes has developed from these original structures through a few “elementary processes” (overtopping, planation, fusion, incurvation, and reduction). In Vererbung “erworbener Eigenschaften” und Auslese (1938, 1969), Zimmermann discussed the factors of evolution and shed a critical light on ambiguous concepts like mutation, purpose, adaptation, orthogenesis, and selection. Since man, too, is a link in evolution and subject to its laws, there are many complex implications for our world view and what should constitute ethical behavior. In Evolution und Naturphilosophie (1968) Zimmermann offers a well-rounded synopsis of these complex issues.
Phylogeny lets us trace the course of transformation, as observed when adult stages are compared. In nature transformation occurs in a chain of consecutive ontogenies. Zimmermann called this entire process “Hologenie”. In order to trace the evolutionary process, he chose the living example of the genus Pulsatilla, which with its numerous primitive characteristics and subspecific taxa, seems to be especially suitable for this purpose. The results of these taxonomical and genetic studies, which he conducted over three decades, have been recorded in numerous publications and are evaluated in his book on the telome theory (1965), as well as in Hegi’s Illustrierte Flora von Mittel-Europa.
Zimmermann’s works are characterized by the clarity of the descriptions and the definitions, the sharp formulation of problems, and the discussion of differing opinions.
Besides being active as a researcher and academic teacher, Zimmermann was an energetic advocate in word and deed for the conservation of nature and the countryside.
I. Original Works. “Die Georeaktionen der Pflanze”, in Ergebnisse der Biologie, 2 (1927), 113-256; Die Phylogenie der Pflanzen (Jena, 1930; 2nd, rev. ed., 1959); “Arbeitsweise der botanischen Phylogenetik” in Emil Abderhalden, ed., Handbuch der biologischen Arbeitsmethoden (Berlin and Vienna, 1931), Abt. 9, teil 3.2, 941-1053; Vererbung “erworbener Eigenschaften” und Auslese (Jena, 1938; 2nd ed., 1969); Grundfragen der Evolution (Frankfurt, 1948); Geschichte der Pflanzen (Stuttgart, 1949; 2nd ed., 1969), also in Spanish, Evolucion vegetal (Barcelona, 1976); Evolution: Die Geschichte ihrer Probleme und Erkenntnisse (Freiburg and Munich, 1953);Die Telomtheorie (Stuttgart, 1965); “Methoden der Evolutions wissenschaft (-Phylogentik)”, in Gerhard Heberer, ed., Die Evolution der Organismen, 3rd ed., I (Stuttgart, 1967), 61-160; Evolution und Naturphilosophie (Berlin, 1968); “Magnoliaceae, Paeoniaceae, Ranunculaceae”, in Gustav Hegi, ed., Illustrierte Flora van zmittel-Europa, III, 3 (Munich, 1974), 36-356.
II. Secondary Literature. K. Mägdefrau, “Walter Zimmermann’s botanisches Werk” in Veröffentlichungen der Landesstelle für Naturschutz Baden-Württemberg, 30 (1962), 10-18 (listing works 1921-1926); and W. Weber, “Walter Zimmermann, Botaniker, Phylogenetiker, Natrschützer”, in Jahreshefte der Gesellschaft für Naturkunde in Württemberg, 137 (1982), 166-171, with a portrait and a list of selected publications.