SCHWENDENER, SIMON

(b. Buchs, St. Gallen [now Aargau], Switzerland, 10 February 1829; d. Berlin, Germany, 27 May 1919), plant anatomy and physiology. For the original article on Schwendener, see DSB, volume 12.

Recent scholarship has brought two aspects of Schwendener’s botanical research to light: his investigations of lichens as component, symbiotic organisms and his mechanical approach to understanding plant anatomy. Though the conclusions he offered in each of these areas drew criticism from his contemporaries, Schwendener was still influential in redirecting investigative botany through his students’ studies of biogeography and adaptation.

Since 1990, Schwendener’s contributions to nineteenth-century botany have been more closely examined. Whereas in the early 1800s botany was dominated by taxonomic concerns and anatomical research, from the late 1830s onward efforts by a handful of botanists, initially led by Matthias Schleiden at Jena, changed the scope of academic botany from plant anatomy and taxonomy to investigations into the biological processes that controlled plant development, reproduction, growth, and nutrition. Schwendener’s research embodies this changing emphasis in two main areas: in his studies of lichens and their implications for symbiosis, and in his physicomechanical approach to plant anatomy.

Study of Lichens Schwendener’s investigations into the physiology of lichens not only changed how botanists classified these puzzling organisms, but also opened new ways into thinking about parasitism and symbiosis. Traditionally, lichens, along with many other newly observed microscopic organisms (including bacteria), had been indiscriminately and inconsistently lumped among the cryptogams—unicellular organisms that lacked differentiated structures (such as algae, fungi, mosses, and some ferns). How to accurately classify and characterize lichens was among the most hotly contested questions in cryptogamic botany in the middle of the century.

During 1868 and 1869 Schwendener published a series of books and papers in which he presented his “dual hypothesis”—that lichens comprised both algae and fungi in a parasitic relationship. Each component of a lichen had a specific physiologic role: the alga contributed carbon dioxide obtained from the air, whereas the fungus contributed water and minerals from soil or other material. From this, Schwendener concluded that lichens were a modified form of fungus. The algae found in lichens, he claimed, were transformed over the course of a few generations of association and were no longer recognizable as individual or distinct organisms. This characterization of fungi drew heavy criticism from some of his colleagues. Cryptogamists who had concentrated their energies upon arguing that lichens were their own distinct group of organisms objected to what they regarded as their reduction to a subdivision of algae or fungi, thus undermining evidence of their distinctiveness from other cryptogams.

In addition, Schwendener had described lichens in social rather than biological terms. Specifically, he regarded the fungi and algae as suspended in a masterslave relationship. The fungi—usually ascomycetes—were predators who enveloped their prey and enslaved them for physiological gain. As Jan Sapp has explained, even botanists who agreed with Schwendener’s dual hypothesis took issue with this slavery metaphor; Johannes Reinke, for example, believed lichens were more accurately described as “cooperative” organisms, rather than as modified fungi.

This distinction, along with the idea that lichens might be a dual or composite organism, gained strength among Schwendener’s students and the students of Anton de Bary at Strassburg (now Strasbourg, France). As Reinke had insisted, isolating the component organisms destroyed the lichen; while it was possible to isolate the algae from lichens, reintroducing algae to their associated fungi did not consistently produce a lichen. These fungi were not easily cultured, which cryptogamists interpreted as evidence that they had adapted so completely to the presence of algae that they were incapable of surviving when isolated. Lichens were therefore confirmed as double organisms, yet also as sufficiently morphologically and physiologically distinct from algae and fungi. This realization necessitated not only a revision of classificatory schema that saw lichens as fungi or intermediate organisms, but also a revision of Schwendener’s conception of the component algae as parasitic “slaves.” This, in turn, prompted cryptogamic physiologist Albert Bernhard Frank to coin a new word in 1877 to describe the relationship—symbiotismus, later popularized by de Bary as symbiosis. Frank used this term to denote the coexistence of organisms without ascribing either a functional role or assuming a parasitic relationship.

Use of the Microscope Like Schleiden and the first generation of cryptogamic physiologists, Schwendener was dissatisfied with what he regarded as outmoded, traditional approaches to plant anatomy. He, too, turned to microscopy as the best means of tackling unanswered questions, and published a treatise on its proper use in botany: Das Mikroskop: Theorie und Anwendung desselben(which he coauthored with Karl von Nägeli), a detailed technical manual for the use of the microscope in botanical investigation. Das Mikroskop included an extensive description of physical optics; a comparison (complete with in-text images and a price list at the end of the book) of the different kinds of microscopes then available, the technical and mechanical differences between them, and the different purposes for which they might be used; and instructions for adjusting for optical aberrations and the vagaries of working with different media, before introducing the microscope’s use in morphological and anatomical study.

But Schwendener’s integration of microscopy into investigative botany was significantly different from that of Schleiden and his colleagues. Whereas the first generation of cryptogamists regarded microscopy as a means of observing physiological processes, Schwendener used microscopy as a means of identifying the principles that regulated the structure and arrangement of plant tissues. He was frustrated with existing morphology and anatomy texts; he dismissed de Bary’s comparative morphology textbooks as outdated and descriptive, and criticized them for their lack of analysis.

Schwendener preferred a method that emphasized interpretation over description and was highly derivative of his background in physics and mechanics. He saw in mechanics the analytical tools and methods that could explain multiple traits of plant anatomy and structure. Early in his career, for example, he conducted what Eugene Cittadino has described as a “detailed mathematical study of periodic phenomena” such as the opening of buds. He expanded his mechanical approach into a search for a general principle that could explain the structure and arrangement of plant tissues. His method was rooted in the conviction that plant structures at the cellular level— that is, the shape and arrangement of individual cells— determined the mechanical and structural properties of plants and their component tissues.

Schwendener described this approach as “physico-mathematical,” that is, a joint physiological and anatomical investigation that could be applied to all tissue systems of a plant and emphasized the relationships between the component tissues of plants and their structural characteristics. The shape and the orientation of cells, he argued, was directly relevant to the mechanical properties of the tissue they constituted—more accurately, the physical properties of the cells determined the physical properties of the tissue. In 1874 Schwendener published Das mechanische Princip im anatomischen Bau der Monocotylen, in which he applied this physicomathematical method to his investigations of the relationship between structural tissue (specifically, sclerenchyma) and responses to physical stress in monocotyledons. he regarded this book as a distinct break from traditional descriptive plant anatomy.

Historical reports of the reception of this volume are somewhat conflicting. De Bary and Julius von Sachs, professor of botany at Würzburg, Germany, supposedly dismissed the volume, yet Cittadino has noted that de Bary declared the book to be “excellent” and was highly complimentary. But Sachs complained that the book was too steeped in mathematics and physics, and that it was not appropriate to describe the tissues on which Schwendener had focused as a “mechanical system.” Other criticisms contended that physiological anatomy was too utilitarian and tended toward the teleological or noted that Schwendener’s plant anatomy was strictly structural; he limited his discussion to mature plants and did not address development—either as a process or its relationship to anatomy—at all.

Though responses to Schwendener’s book may have been mixed, his students—Gottlieb Haberlandt in particular—enthusiastically applied physicomathematical anatomy to research questions in many different areas of botany. Topics such as the mechanical aspects of dissemination of fruits and seeds, the mechanism of coiling in climbing plants, and the effects of exposure to weight on wood growth were among those investigated by his students at the Berlin Botanical Institute.

But the implications of Schwendener’s plant anatomy went beyond the properties of specific tissues and extended to questions of structural adaptation and evolution as well. Even so, as Cittadino has noted, this was not as much the result of Darwinian thought as it was a continuation of Schwendener’s interest in structure with respect to function. Schwendener was critical of natural selection, and instead argued that internal forces, not environmental pressures, drove evolutionary change. As such, adaptation was a highly individualized, mechanical process, and in the 1880s Schwendener took special interest in the relationship between specific anatomical features of plants and environmental conditions. This interest, in turn, led him to encourage his students to pursue field research.

Schwendener as Educator At Berlin, Schwendener’s students formed a close-knit group of botanists whose enthusiasm for “physiologische Pflanzenanatomie” dominated the Botanical Institute in the late 1870s and 1880s. Many of his students faced the same sort of criticisms that Schwendener’s own work had drawn, yet remained undaunted in their pursuits. Schwendener’s teaching style likely strengthened both his students’ sense of camaraderie and their dedication to their work; though he continued writing theoretical papers and books while at Berlin, he conducted no new research, and instead involved himself in his students’ investigations. He emphasized inductive, experimental study over rote learning, and often discouraged his students from surveying published literature until they had conducted their own experiments. Schwendener also insisted that fieldwork was essential to understanding adaptation as the product of both structure and function. Only firsthand knowledge of the conditions in which plants lived could support theoretical claims about adaptation, and many of his students undertook field studies within Germany and abroad. Cittadino has examined the importance of Schwendener’s students and their field research in the expansion of Darwinian thought in Germany; in addition, such research expanded the scope of biogeography as botanists identified new ways of interpreting the relationship between a region’s climate and its vegetation, and also contributed to the development of ecology as a discipline in the late 1870s and 1880s.

SUPPLEMENTARY BIBLIOGRAPHY

WORKS BY SCHWENDENER

With Karl Wilhelm von Nägeli. Das Mikroskop: Theorie und Anwendung desselben. Leipzig, Germany: W. Engelmann, 1865.

“Die Flechten als Parasiten der Algen.” In Verhandlungen der Schweizerischen Naturforschenden Gesellschaft5 (1869): 527–550. Presents additional information about his interpretation of the nature of lichens and their associated fungi.

Das mechanische Princip im anatomischen Bau der Monocotylen. Leipzig, Germany: W. Engelmann, 1874.

Schwendeners Vorlesungen über mechanische Probleme der Botanik gehalten an der Universität Berlin. Edited by Carl Holtermann. Leipzig, Germany: W. Englemann, 1909. Offers a general overview of Schwendener’s physicomathematical botany and illustrates the detailed mathematics he utilized in his physiological investigations.

OTHER SOURCES

Cittadino, Eugene. Nature as the Laboratory: Darwinian Plant Ecology in the German Empire, 1880–1900. Cambridge, U.K.: Cambridge University Press, 1990. Examines the significance of Schwendener’s physicomathematical plant anatomy in the broader context of Darwinian adaptation and the expansion of German botany in the late nineteenth century.

Haberlandt, Gottlieb. “Das Pflanzenphysiologische Institut der Universität Berlin, zur Einführung.” In Beiträge zur Allgemeinen Botanik, vol. 1, edited by Gottlieb Haberlandt. Berlin: Gebrüder Borntraeger1918. Chronicles the development of the Berlin Botanical Institute, in which Schwendener figures prominently.

Jahn, Ilse, and Ulrich Sucker. “Zur Geschichte der Botanik an der Berliner Universität von 1810 bis 1945.” Wissenschaftliche Zeitschrift der Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Reihe34, nos. 3/4 (1985): 189–202.

Sapp, Jan. Evolution by Association: A History of Symbiosis. Oxford: Oxford University Press, 1994. Provides a short but thorough synopsis of Schwendener’s research on lichens and their implication for later studies of symbiosis.

Christina Matta