SCHLEIDEN, MATTHIAS JACOB

(b. Hamburg, Germany, 5 April 1804; d. Frankfurt am Main, Germany, 23 June 1881),

botany, cell theory, philosophy of science, science popularization, developmental morphology, plant physiology. For the original article on Schleiden see DSB, vol. 12.

Analyses in the late twentieth and early twenty-first centuries reveal that many concepts important to Schleiden’s mature cell theory were already present in his earlier work. He would give to cells the same roles that he (and others) earlier assigned to structures such as sprouts, leaves, and pollen. Both before and after he focused on the cell, he was answering questions about generation and morphology by tracing diverse forms and processes back to common origins. Scholars have also unearthed more details about his career and analyzed his other writings, especially his inductive philosophy of science.

Beginnings: Morphology and Generation While a medical student in Göttingen (1832–1835), Schleiden was initially more interested in physical sciences and their philosophical foundations. A course with Gottlob Bartling got him interested in plant microscopy. In 1835 he continued his studies in Berlin, working chiefly with his uncle Johann Horkel (a former student of Johann Christian Reil), who advocated the study of embryos and denied that plants reproduced by sexual mixture — both key ideas for the nephew as well.

Recent research elucidates how Schleiden’s morphology shaped his interpretation of pollen and cells. He began with a critique of Johann Wolfgang Goethe. The poet and other morphologists observed the variety of macroscopic structures such as stamens and leaves (both on the same plant and on different kinds of plants), yet tried to connect those many forms to a few spatial concepts; for instance, they likened a stamen to a contracted version of the basic leaf shape.

Schleiden continued their search for unity underlying diversity, but with different methods and results. Even though Goethe had made many observations, in 1837 Schleiden dismissed his morphology as speculation because Goethe had tried to relate organs by visualizing in the mind geometrical variants of mature shapes. Schleiden insisted true inductive morphology must seek a relation observable in the world: the developmental continuity between earlier and later structures in the life of a plant.

The first stages of plants were the most important objects of observation. Botanists could see fundamental similarities between plant parts by tracing them back to similar embryonic origins—even if the later forms looked very different. Citing Caspar Friedrich Wolff, Schleiden wrote that everything else developed from the initial sprout which comprised the fundamental organs (Grun-dorgane) stem and leaves.

What, in turn, gave rise to that sprout? The role—or even necessity—of pollen in fertilization had long been controversial. In the eighteenth century, Carl Linnaeus taught that all plants reproduced sexually: higher plants with flowers or other visible sex organs he called phanerogams; lower plants (in which he included ferns, mosses, algae, and fungi) he called cryptogams because their sexuality was hidden. Other botanists attributed sex to phanerogams but thought cryptogams produced only asexual spores. Higher plants were the model, lower ones merely deviant or lacking.

By the 1830s Robert Brown and other botanists had observed pollen tubes extending toward the ovule, but what happened when the pollen arrived was still not clear. Schleiden agreed with Horkel’s observation that the pollen tube wall remained intact rather than fusing with anything in the ovule. The nephew defied tradition by using cryptogams as models for phanerogams: spores sprouted and grew by taking up nutrient fluids from the soil; pollen was a spore that needed the special environment and more refined sap in the ovule. Since leaf tissue in some plants directly gave rise to new sprouts, in some became spores, and in some became pollen, all three were equivalent. (Even when he abandoned his pollen theory Schleiden still extrapolated from the simplest cryptogams to phanerogams [1861].) Botanists have rejected details of Schleiden’s pollen observations, but the cryptogam model, including the analogy of pollen grains to spores, remains essential to plant physiology and classification.

Schleiden also united the seemingly different processes of development and reproduction. Like leaf tissue that budded directly, a pollen grain or spore was both a continuation of growth and the germ that became the future plant. Schleiden called the pollen/embryo a leaf cell grafted onto the stem (ovule) (1837, p. 313). Reproduction by grafting may have connected Schleiden’s understanding of growth to older views of the plant as an aggregate of individuals sprouting within individuals. Some earlier thinkers had interpreted each new sprout on a tree as an individual plant, as if it had been grafted on the stem. Although Schleiden’s article on cell theory did not explicitly invoke grafting, he did describe the woody tree trunk “as if it were a mere organized soil” upon which a new generation of sprouts grew (1838, p. 171; 1847 p. 260). He wrote positively of theories that the annual buds on a tree were individuals, even though he said strictly speaking only cells qualified as individuals (1838, pp. 168–174; 1847, pp. 258–263). Development connected these two kinds of individuals: every sprout was traceable back to a cell.

Cells: The New Grundorgane In the 1837 paper cells were occasionally mentioned but were not yet the star of the show. In 1838 Schleiden put the cell into the role of Grundorgan. He praised Julius Meyen as an observer of mature plant microanatomy, but dismissed his and others’ work as irrelevant because it did not study development. In contrast Schleiden considered the crucial prerequisite to his cell theory to have been Robert Brown’s calling attention to nuclei. Brown had noted the frequent (not universal) presence of a structure he called the “nucleus of the cell” (Schleiden 1838, p. 139; 1847, p. 233). After meeting with Brown in 1836, Schleiden noticed that nuclei were the first structures to develop in the embryo and that cells formed around them. He propounded the first cell theory that gave an essential role to the nucleus.

Schleiden insisted that the same law of cell formation operated in later tissues, even in cases where he had difficulty observing them. The formation of cells within cells became the fundamental process in all development. Like the earlier theories in which new individuals sprouted on trees, Schleiden saw growth as the reiteration of reproduction. Each cell was the first stage in the life of an individual, whether it remained a single cell, or became leaves, spores, or trees. In one sense Schleiden broke the plant into individual cells; in another he asserted an essential similarity among cells, pollen, and whole plants.

The cellular beginnings of organisms would also justify extrapolating cell theory beyond plants. After Schleiden told Theodor Schwann about nuclei forming cells, Schwann recognized a similar process as fundamental to animal development, and compared cell formation to crystallization (1839). Some have suggested Schleiden also based his cell formation theory on crystallization. But the botanist originally said that cell formation made plants different from crystals or animals (1838, p. 161; 1847, p. 251). Analogies between crystallization and development are older than Schleiden (e.g., Fries), but only after Schwann suggested cells as the bridge between them did the botanist (in his textbook) praise the analogy, though with emphasis on the differences.

Induction: Key Observations and Extrapolation The methodological introduction to Schleiden’s textbook (1842) went beyond merely denouncing speculation or defending particular observations. It formally connected his emphasis on development and cells to the inductive principles of Jakob Friedrich Fries. Even before becoming a microscopist Schleiden had admired the philosopher Fries, “from whose logic I have learned as much botany as from all botanical writings together” (Lorch, p. xiii, translating Schleiden, 1850, p. 115). Schleiden drew upon Fries not for specifics about plants but for philosophical ideas about unifying physics and physiology, separating spirit from material (e.g., ideas do not cause physical

phenomena), and “rational induction” guided by regulative “leading principles.”

In philosophy of science, induction refers to systematic observation leading to general principles based on those observations. As discussed above, Schleiden considered some observations more illuminating than others. Underlying affinities between mature specimens often could not be seen in the specimens themselves; morphologists had to look elsewhere. Goethe used the mind’s eye to see the ideal plant form; Schleiden used the microscope to see the embryonic primordia. He pointed to those primordia to defend parallels across different plant taxa. Spores and pollen did not develop into one another within the same plant, but both could be traced back to the same kind of beginning.

Schleiden did refer to development within the same plant when he extrapolated his theory of cell formation from embryos to later tissues. Since pollen, embryos, and leaves were the same object, just at different times, “we may certainly infer” that the formation process observed in embryos also took place in later tissues (1838, p. 164; 1847, p. 254). Here Schleiden made a sort of bootstrapping move: his critique of Goethe had defended the study of development because it was observable, but his cell theory used development to infer beyond what was observable. (In the 1840s Karl Nägeli would overturn Schleiden’s cell formation theory by showing that embryonic tissue in fact displayed cell formation not typical of later tissues.)

In Ulrich Charpa’s felicitous phrase, Schleiden’s methodological introduction to his textbook prescribed virtues for explorers who needed to rely on the honesty and the theoretical and practical expertise of fellow microscopists and instrument makers. The artisan Carl Zeiss was among those who learned microscopy at the physiology institute that Schleiden cofounded in 1845. Later Schleiden helped Zeiss start his business and endorsed its microscopes. Schleiden directed his textbook remarks about microscopy mainly to warn practitioners about potential pitfalls (including flawed instruments); in brief remarks to skeptics of microscopy, he put the blame for error on the observer, not the tool. Schleiden emphasized skill to justify his new discipline and to exclude other microscopists. Only through long training could one come to understand the optical properties of good (and bad) microscopes, develop dexterity in preparation techniques such as cutting specimens, and learn to convey careful interpretative observation by accurate drawings.

Later Career and Writings Schleiden proclaimed his developmental morphology, including cell and pollen theories, while a medical student in Berlin in the late 1830s. In 1839 he became (extraordinary) professor of natural history in the philosophical faculty at Jena, where he received his philosophy degree. In 1843 Tübingen granted him an honorary MD. In 1844 he married Bertha Mirus (d. 1854), with whom he had three daughters. In 1855 he married Therese Marezoll, who survived him.

Schleiden’s most successful course at Jena was originally called comparative physiology. It covered function and development of organisms (including the work of Johannes Müller), physical anthropology (based on Johann Friedrich Blumenbach), and Fries’s theory of the human mind. (Schleiden’s reading about ethnography would contribute to some of his much later writings.)

The medical faculty complained about a professor in the philosophical faculty encroaching on their prerogative to teach human physiology, so he renamed the course “Anthropologie.” Schleiden further offended the medical faculty by teaching pharmacological botany and laboratory practica in physiology. Such turf battles (and other universities’ interest in hiring him) led the authorities in Weimar to move Schleiden to the medical faculty in 1846, where he became a full professor in 1849. In 1851 he became director of the botanical garden, but he never held the title professor of botany.

In the 1840s Schleiden also worked on the application of plant chemistry and physiology to agriculture. He rejected vitalism but put limits on the value of chemistry for botany. In 1840 Justus Liebig wrote that a chemistry laboratory was the best place to learn plant physiology. Schleiden retorted that Liebig lacked the philosophical sophistication and the knowledge of cell theory to study plants.

His writings after he left Jena have not as of 2007 been studied in depth, but historians have noted some continuing themes, including anthropology, biological development, and Friesian neo-Kantian philosophy. Already endorsing species transformation in the 1840s, Schleiden was one of the first German scientists to praise Darwinism, and produced books summarizing research on the physical and cultural anthropology of early humans. His last works, monographs on the rose and salt, were intended for scholarly audiences and combined the science and the cultural position of their subjects.

At his death he left an unpublished manuscript on religion. Initially not particularly religious, in 1839 he had adopted orthodox Lutheranism when recovering from a suicidal depression. In botanical lectures in 1840s and his denunciation of materialism in 1863 he insisted that the spiritual and physical worlds both existed but did not causally interact. By his later years he had moved to a unitarianism that he no longer considered Christian.

SUPPLEMENTARY BIBLIOGRAPHY

Almost everything ever written by or about Schleiden or Fries can be found in Glasmacher (1989). Mylott (2002) also has an extensive bibliography. Archival and published sources are listed in Jahn and Schmidt’s biography (2006).

WORKS BY SCHLEIDEN

“Einige Blicke auf die Entwicklungsgeschichte des vegetabilischen Organismus bei den Phanerogamen” [A few views of developmental history of the vegetable organism in the phanerogams]. Wiegmann’s Archiv für Naturgschichte 3, no.1 (1837): 289–320. Morphology, including critique of Goethe, and brief statement of pollen theory.

“Beiträge zur Phytogenesis.” Müller’s Archiv für Anatomie, Physiologie, und wissenschaftliche Medicin, 1838: 137–176. Translated as “Contributions to Our Knowledge of Phytogenesis” in Scientific Memoirs, edited by Richard Taylor et al., vol. 2, part 6. London: Taylor, 1841. German version republished with additional notes in Schleiden, Beiträge zur Botanik, vol. 1. 1844. The revised version is reprinted in Klassische Schriften zur Zellenlehre, edited by Ilse Jahn. Leipzig: Geest & Portig, 1987. Revised version also translated as “Contributions to Phytogenesis” in Smith (1847), which also includes Schwann’s book. This article is the classic statement of Schleiden’s cell theory.

Grundzüge der Wissenschaftlichen Botanik. 1st ed., 2 vols. Leipzig: Wilhelm Engelmann, 1842 and 1843. Revised ed. 1845 and 1846. First part of 2nd ed. reprinted, edited by Olaf Breidbach. Hildesheim: Georg Olms Verlag, 1998. 3rd ed., 1849 and 1850; 4th ed., 1861. The methodological introduction from the 4th ed. (virtually unchanged from 2nd ed.) is reprinted in Charpa (1989). Textbook.

Principles of Scientific Botany or Botany as an Inductive Science. Translation of 2nd ed. of Grundzüge der Wissenschaftlichen Botanik, by Edwin Lankester, 1849. Reprint, with an introduction by Jacob Lorch. New York: Johnson Reprint Corporation, 1969. This is a translation of the technical botanical content of the Grundzüge. As of 2007, no English translation exists of the textbook’s “Methodologische Grundlage”; Lankester translated only some remarks on the use of the microscope and a two-page methodological summary from another work by Schleiden.

OTHER SOURCES

Brown, Robert. Observations on the Organs and Mode of Fecundation in Orchideae and Æsclepiadeae, 1831. Reprinted with minor revisions as “Observations on the Organs and Mode of Fecundation in Orchideae and Æsclepiadeae.” Transactions of the Linnean Society of London 16 (1833): 685–742; article reprinted in The Miscellaneous Botanical Works of Robert Brown, vol. 1. Edited by John J. Bennett. Includes appendix about the cell nucleus.

Buchdahl, Gerd. “Leading Principles and Induction: The Methodology of Matthias Schleiden.” In Foundations of Scientific Method: The Nineteenth Century, edited by Ronald N. Giere and Richard S. Westfall. Bloomington: Indiana University Press, 1973. German version in Charpa, 1989. Schleiden’s neo-Kantian philosophy.

Charpa, Ulrich, ed. Wissenschaftsphilosophische Schriften, by M. J. Schleiden. Cologne: Jürgen Dinter Verlag für Philosophie, 1989. Schleiden’s essential philosophical writings, with commentaries.

———. “Matthias Jakob Schleiden (1804–1881): The History of Jewish Interest in Science and the Methodology of Microscopic Botany.” Aleph: Historical Studies in Science and Judaism 3 (2003): 213–245.

———. “Matthias Jacob Schleiden.” In Naturphilosophie nach Schelling, edited by Thomas Bach and Olaf Breidbach. Stuttgart: Frommann-Holzboog, 2005.

de Chadarevian, Soraya. “Instruments, Illustrations, Skills, and Laboratories in Nineteenth-Century German Botany.” In Non-verbal Communication in Science Prior to 1900, edited by Renato G. Mazzolini. Firenze: Olschki, 1993. Schleiden demarcating his discipline.

Duchesneau, François. Genèse de la théorie cellulaire. Collections Analytiques 1. Montréal: Bellarmin, 1987. Mainly about situating Schwann with respect to nineteenth-century zoological research programs; one chapter on Schleiden.

Farley, John. Gametes and Spores: Ideas about Sexual Reproduction, 1750–1914. Baltimore: Johns Hopkins University Press, 1982. Includes a chapter on Schleiden’s pollen theory.

Glasmacher, Thomas. Fries – Apelt – Schleiden: Verzeichnis der Primär- und Sekundärliteratur, 1798–1988. Cologne: Jürgen Dinter Verlag für Philosophie, 1989.

Goethe, Johann Wolfgang von. “Die Metamorphose der Pflanzen,” 1790. Reprinted in Die Schriften zur Naturwissenschaft, vol. 9, Morphologische Hefte, edited by Dorothea Kuhn. Weimar: Hermann Bohlaus Nachfolger, 1954. Translated by Bertha Mueller as “The Metamorphosis Grundzüge der Wissenschaftlichen Botanik. 1st ed., 2 vols. Leipzig: Wilhelm Engelmann, 1842 and 1843. Revised ed. 1845 and 1846. First part of 2nd ed. reprinted, edited by Olaf Breidbach. Hildesheim: Georg Olms Verlag, 1998. 3rd ed., 1849 and 1850; 4th ed., 1861. The methodological of Plants” in Goethe’s Botanical Writings. University Press of Hawaii, 1952. Reprint, Woodbridge, CT: Ox Bow Press, 1989. One of the founding documents of morphology.

Horkel, Johann. “Eine historische Einleitung in die Lehre von den Pollenschläuchen.” Summary report of address to the academy. Bericht über die zur Bekanntmachung geeigneten Verhandlungen der Königlichen Preussischen Akademie der Wissenschaften zu Berlin 1 (1836): 71–82. Describes and evaluates the observations of various researchers, including Brown and Schleiden.

Jahn, Ilse, and Isolde Schmidt. Matthias Jacob Schleiden (1804–1881): Sein Leben in Selbstzeugnissen. Halle: Leopoldina, 2006. Most extensive biography.

Mazumdar, Pauline M. H. Species and Specificity: An Interpretation of the History of Immunology. Cambridge, U.K.: Cambridge University Press, 1995. Schleiden emphasized unity rather than diversity of living things.

Mendelsohn, Andrew. “Lives of the Cell.” Journal of the History of Biology 36 (2003): 1–37. A delight to read; applies many science studies insights to nineteenth-century cell theory and induction from exemplars.

Mylott, Anne. “Cells, Life Force, and Reductionism in the Botany of Matthias Jacob Schleiden.” In Ideengeschichte und Wissenschaftsphilosophie: Festschrift für Lutz Geldsetzer, edited by Richard Dodel, Esther Seidel, and Larry Steindler. Cologne: Jürgen Dinter Verlag für Philosophie, 1997. Schleiden’s Friesian philosophy and his argument with Liebig.

———. “The Roots of Cell Theory in Sap, Spores, and Schleiden.” PhD diss., Indiana University, Bloomington, 2002. Analyzes his morphology, pollen, and cell theories, and relates his philosophy to his biology. Also covers some predecessors, including Henri Dutrochet and Franz Julius Ferdinand Meyen.

Nyhart, Lynn. Biology Takes Form: Animal Morphology and the German Universities, 1800–1900. Chicago: University of Chicago Press, 1995. Meaning of “Grund” and “Physiologie,” as well as morphology.

Ratzeburg, Julius Theodor Christian. Forstwissenschaftliches Schriftsteller-Lexikon. Berlin: Nicolai, 1872. Unsympathetic portrait of Schleiden. Most detailed account of Horkel available.

Schickore, Jutta. The Microscope and the Eye: A History of Reflections, 1740–1870. Chicago: University of Chicago Press, 2007.

Schwann, Theodor. Mikroskopische Untersuchungen über die Übereinstimmung in der Struktur und dem Wachsthum der Thiere und Pflanzen, 1839. Portions reprinted in Jahn (1987). Translated by Henry Smith as Microscopical Researches into the Accordance in the Structure and Growth of Animals and Plants. 1847. Classic of the cell theory.

Werner, Petra, and Frederic L. Holmes. “Justus Liebig and the Plant Physiologists.” Journal of the History of Biology 35 (2002): 421–441.

Anne Mylott