SCHLEIDEN, JACOB MATHIAS

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

botany, natural science, scientific popularization.

Schleiden came from a well-to-do family: his father was municipal physician of Hamburg. After legal studies, culminating in a doctorate, at the University of Heidelberg (1824–1827), Schleiden established a legal practice in Hamburg. He was dissatisfied, however, and, after a period of deep depression, he abandoned this profession. In 1833 he began to study natural science at Göttingen and then transferred to Berlin. He devoted himself enthusiastically to the subject of botany, in which he was encouraged by his botanist uncle, Johann Horkel, to whom he remained forever grateful. During these years Alexander von Humboldt and Robert Brown were resident at Berlin. Schleiden worked in the laboratory of the celebrated physiologist Johannes Müller, and there he met Theodor Schwann. In this inspiring milieu, Schleiden worked intensively and produced noteworthy publications. He obtained his doctorate in 1839 at Jena and was then able to give free reign to his pedagogical fervor. He lectured and wrote both technical and popular scientific works on the widest range of topics.

Schleiden’s lectures drew enthusiastic, overflow audiences; his numerous articles appeared in highly respected journals, or in collections that were often reprinted and translated. He declined an offer from the University of Giessen in 1846, but in 1850 he accepted nomination as titular professor of botany at Jena. He also received many honors from learned societies. In spite of his success. Schleiden decided to leave Jena. His combative personality probably contributed to this decision: he was often involved in polemics with leading figures of the day. Also, he had an insatiable desire to study problems going beyond the confines of botany and natural history. He soon became a highly regarded popular lecturer and writer; indeed, he was one of the most successful popularizers of the age–no small achievement at a time when scientists like Virchow, Helmholtz, Liebig, Moleschott, Alexander von Humboldt, and Ludwig Büchner, among others, were addressing the general public. Following his departure from Jena in 1862 and a stay at Dresden, Schleiden became professor of anthropology at Dorpat. Even though he soon left Dorpat, the Russian government granted him a pension. He became a Privatgelehrter and thereafter frequently moved from one city to another.

In 1838 Schleiden published “Beiträge zur Phytogenesis” in Müller’s Archiv, one of the most respected journals of the time. This article, which was immediately translated into French and English, fixed his name in the history of biology. According to a well-known tradition, the cell theory was conceived in a conversation between Schleiden and Schwann on the subject of phytogenesis. In fact, however, historical investigation has shown that Schleiden’s article, like Schwann’s book, represents only one stage–although admittedly and important one–in the evolution of the search for the elementary unit common to the animal and plant kingdoms. (On this subject see the publications of Studnička, Klein, Baker, and Florkin: the biographies in this Dictionary of Mohl, Oken, Raspail, and Schwann, among others, should also be consulted.)

Schleiden reprinted the article in a collection of studies and dealt at length with its contents in his textbook on botany. In the article, which evoked wide interest and sparked violent debates, Schleiden starts from Robert Brown’s discovery of the cell nucleus (1832), which Schleiden called the cytoblast, and then indicates its role in the formation of cells. According to Schleiden, as soon as the cytoblast reaches its final size, a fine, transparent vesicle forms around it: this is the new cell. The cell then crystallizes within a formative liquid. The best statement of this interpretation can be found in his botany textbook, Grundzüge der wissenschaftlichen Botanik (1842); “Since the elementary organic cells present a marked individualization and since they are the most general expression of the concept of the plant, it is necessary, first of all, to study this cell as the foundation of the vegetable world. We have therefore produced a study of the vegetable cell.” This clearly announced the advent of plant cytology. This subject became the starting point of all subsequent botany textbooks. As Schleiden stated, the cells can form only in a liquid containing sugar, gum, and mucus (cytoblastema). This phenomenon occurs in the following manner: the mucous portion condenses into more or less round corpuscles (cytoblastus). On its surface, a part of the liquid is transformed into jelly, a relatively insoluble substance: thus there is created a closed gelatinous vesicle that is penetrated by the external liquid... . During the progressive expansion of the vesicle, the jelly of the wall is generally transformed into a membranous substance and the formation of the cell (cellula) is completed.

Schleiden’s interpretation merits careful attention. The idea that cells are crystallized inside an amorphous primary substance is as old as the study of the cell itself. The idea can be traced back to the writings of Grew (1675), who compared the process with the fermentation of a paste or liquid. It appears again, independently, in Raspail, as a vesicular crystallization. Mohl observed cell division but was undecided in his views on the existence of “the free formation of cells,” as this type of process was long called. Despite increasing evidence of nuclear activity during division, and despite Virchow’s definitive aphorism, “omnis cellula a cellula,” the notion of the formative blastema long survived, owing mainly to the support of Charles Robin. An eminent figure in the development of the subject of microscopic anatomy, Robin remained faithful to the notion, granting the cell a position of no special distinction among the anatomical elements of the higher organisms (see Klein, 1936: 1960).

From the start of his career, Schleiden showed a predilection for the microscope, and he contributed greatly to its introduction in biological research. He engaged in long and sometimes bitter disputes with Amici, one of the outstanding micrographers and opticians of the period. Schleiden is thought to have played an active role in the establishment of the Zeiss optical works in Jena.

Schleiden based his description of cytogenesis on an examination of the pollen tube. Ironically, his interpretation of this tube was fundamentally wrong, both morphologically and biologically: he considered it a female reproductive element in the plant. This error, like the one concerning the free genesis of cells, gave rise to much further research and to violent controversies; but one may truly call both these mistakes fruitful.

Schleiden’s botany textbook merits an extensive methodological discussion, but we shall restrict our comments to a few essential points. A number of Schleiden’s articles contain virulent criticism of the botanists of the first half of the nineteenth century, many of whom still upheld the ideas of nature philosophy, against which his textbook was a frontal attack. More important, however, it introduced new pedagogical standards that were to dominate the teaching of botany for years. Beginning with the second edition, the work bore the subtitle Botanik als inductive Wissenschaft.

Schleiden considered the inductive method the only valid one in biology, and the first part of his book constitutes an important document for the study of the methodology of natural history. He declared himself an enemy of all philosophical speculation, while at the same time adhering to the views of Kant and rejecting the label of materialist. He completed his attacks against the philosophers with a brief polemical monograph against the philosophy of Schelling and of Hegel. The entire structure of Schleiden’s textbook was fundamentally new. The lengthy work begins with a study of the material elements of the plant. Next there is a large section on plant cytology, and then a treatment of morphology and organology. The book, which established the teaching of botany on a completely new basis, was often reprinted and appeared in various translations and adaptations. To appreciate the enthusiasm it aroused and its influence in turning young men to the study of botany, it is necessary to read the testimony of contemporaries, particularly of Julius Sachs, a famous botanist and author of a well-known history of botany.

Schleiden’s pedagogical genius manifested itself in other publications as well. From the time of its founding in 1857, Schleiden was an assiduous contributor to Westermann’s Monatshefte, a periodical that maintained high literary and scientific standards. His lectures, delivered to vast audiences, were occasionally published in book form and met with great success. Among the best known of these collections was Die Pflanze und ihr Leben, which was handsomely reproduced and reprinted many times. Another, somewhat more difficult series, Wissenschaftliche Studien, covered a wide range of topics in natural history. Later, Schleiden devoted entire monographs to subjects of apparently limited scope–for example, one to the rose and another to salt, in which he discussed its history, symbolism, and economic and social importance to human life. In other writings he dealt with the Isthmus of Suez and with anthropological questions. Among his last publications were scholarly studies on the fate of the Jews in the Middle Ages, on their martyrdom, and on their importance in transmitting knowledge to the Occident. These works, which were reprinted and translated, stimulated much interest; they also testify to the liberality of Schleiden’s thinking in a period that witnessed the first anti-Semitic campaigns in the universities of Wilhelmine Germany.

This very liberality, however, joined with his combative nature, constantly involved Schleiden in debates and harsh polemics with the most eminent scientists and thinkers of the age, among whom were Amici, Fechner, Liebig, Mohl, Nees von Esenbeck, and Schelling. A few words may be said about his controversy with Fechner. The celebrated founder of modern psychophysiology, convinced of the existence of a soul in all living creatures, had published a work entitled Nanna or the Soul of the Plants. Schleiden violently attacked it, and Fechner responded with a book that is still delightful to read, Professor Schleiden and the Moon. But it should be noted that Schleiden often cut polemics short by the simple expedient of silence.

One of his early biographers, L. Errera, has a neat epitome of his career: “As a popularizer he was a model, as a scientist an initiator.”

BIBLIOGRAPHY

I. Original Works. A list of Schleiden’s writings is given by Möbius (see below). The following works are cited in the text: “Beiträge zur Phytogenesis,” in Archiv für Anatomie, Physiologie und wissenschaftliche Medicin (1838), 137–176, with French trans. in Annales des sciences naturelles. Botanique, 11 (1839), 242–252, 362–370, and English trans. in Scientific Memoirs, 2 (1841), 281–312; Grundzüge der wissenschaftlichen Botanik, 2 vols. (Leipzig, 1842–1843), 2nd ed., Die Botanik als inductive Wissenschaft behandelt (Leipzig, 1845–1846), 3rd ed., Die Botanik als inductive Wissenschaft. Grundzüge der wissenschaftlichen Botanik nebst einer Einleitung als Anleitung zum Studium der Pflanzen (Leipzig, 1849): vol. I , Methodologische Grundlage, Vegetabilische Stofflehre. Die Lehre von der Pflanzenzellen, vol. II , Morphologie, Organologie, with 153 figs. and 4 plates, 4th ed. (Leipzig, 1861); English trans. by E. Lankester as Principles of Scientific Botany as an Inductive Science (London, 1849; 2nd ed., 1868), facs. ed. by Lorch (see below).

See also Beiträge zur Botanik. Gesammelte Aufsätze (Leipzig, 1844); Schelling’s und Hegel’s Verhältniss zur Naturwissenschaft (Leipzig, 1844); Die Pflanze und ihr Leben. Populäre Vorträge (Leipzig, 1848; 5th ed., 1858), also translated into English (1848), French (1859), and Dutch (1873); Studien. Populäre Vorträge (Leipzig, 1855; 2nd ed., 1857); “Über den Materialismus unserer Zeit: Zerstreute Gedanken,” in Westermanns Monatshefte, 1 (1857), 37–45; “Die Landenge von Suez und der Auszug der Isräeliten aus Egypten,” ibid., 4 (1858), 262–273; “Ueber die Anthropologie als Grundlage für alle übrigen Wissenschaften, wie überhaupt der Menschenbildung,” ibid., 11 (1862), 49–58; Das Salz. Seine Geschichte. Seine Symbolik und seine Bedeutung im Menschenleben. Eine monographische Skizze (Leipzig, 1875); “Die Bedeutung der Juden für Erhaltung und Wiederbelebung der Wissenschaften im Mittelalter,” inn Westermanus Monatshefte, 41 (1877). 52–60, 156–169; and “Die Romantik des Martyriums bei den Juden im Mittelalter,” ibid., 44 (1878), 62–79, 166–178.

II. Secondary Literature. On Schleiden and his work, see J. R. Baker, “The Cell Theory, a Restatement. History and Critique,” in Quarterly Journal of Microscopical Science, 89 (1948), 103–125; 90 (1949), 87–108, 331: 93 (1952), 157–190: 94 (1953), 407–440: 96 (1955), 449–481; L. Errera, “J. M. Schleiden,” in Revue scientifique de la France et de l’étranger, 3rd ser., 2 (1882), 289–298: G. T. Fechner, Professor Schleiden und der Mond (Leipzig, 1856); M. Florkin, Naissance et déviation de la théorie cellulaire dans l’oeuvre de Théodore Schwann (Paris, 1960), 57, 62; E. Hallier, “Mathias Jacob Scghleiden. Seine Bedeutung für das wissenschaftliche Leben der Gegenwart geschildert,” in Westermanns Monatshefte, 51 (1882), 348–358: M. Klein, Histoire des origines de la théorie cellulaire (Paris, 1936), 36–39; A la recherche de l’unité élémentaire des organismes vivants. Histoire de la théorie cellulaire (Paris, 1960), 18: J. Lorch, Introduction to Principles Botany as urn Inductive Science by Mathias Jacob Schleiden, Sources if Science, no. 40 (New York-London, 1969), i–xxxiv, a facs, ed. of the London 1849 ed.; M. Möbius, Mathias Jacob Schleiden (Leipzig, 1904); E. Nordenskjöld, Die Geschichte der Biologie (Jena, 1926), 396–401: C. Robin, Anatomie et Physiologie cellulaires (Paris, 1873), 565 ff.; J. Sachs, Geschichte der Botanik (Munich, 1875), 202–207, 349; F. L. Studnička, “Mathias Jacob Schleiden und die Zelltheorie von Theodor Schwann,” in Anatomischer Anzeiger, 76 (1933), 80–95: and A. Wartenberg, “Mathias Jacob Schleiden,” H. Freund and A. Berg, eds., in Geschichte der Mikroskopie, 1 (1963), 299–302.

Marc Klein