Hugo von Mohl

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(b. Stuttgart, Germany, 8 April 1805; d. Tübingen, Germany, 1 April 1872)


Born into a respected bourgeois family, Mohl had three brothers who gained reputations in scholarship, economics, and politics; his brother Jules, a naturalized Frenchman, was professor of Persian at the Collège de France from 1847 to 1876 (on the Mohl brothers see Vapereau [1870]). Mohl had a classical education; but from an early age he demonstrated a predilection for science, especially for botany and optics, thus early revealing his vocation: it was in the field of microscopic botany that he made his most remarkable contributions. He studied medicine at Tübingen and in 1827 presented a work on the structure and movement of the climbing plants, a problem which concerned botanists throughout the nineteenth century. Mohl’s doctoral thesis (1828) was devoted to the constitution of the pores of plants. In 1832 he was appointed professor of physiology at Bern and in 1835 professor of botany at Tübingen, a chair he occupied until his death.

Mohl’s scientific work deals with extremely diverse areas of botany. Among them he devoted himself to the technical problems of the microscope that he himself was able to construct and recorded his findings in a manual on microscopy (1846).

After a century Mohl remains famous for his works on the microscopic anatomy of plants and for his contributions to knowledge of the plant cell. The publication which gives the best picture of his way of working and thinking is the comprehensive memoir “Die vegetabilische Zelle” (1853), in Wagner’s Handwörterbuch der Physiologie, a classic reference work of the period. In this study Mohl sketched a veritable panorama of botany, taking as a base the cell, which he viewed as an “elementary organ.” He summarized his own work, claiming priority in certain cases, and subjected the publications of his predecessors and contemporaries to a critical examination. He recalled that he was the first to demonstrate the fusion of aligned cells in the formation of ducts and to observe intracellular movements. He examined the structure of the cell and its derivatives, its generation by division or free formation, and its physiology as an organ of nutrition, of reproduction, and of movement. For Mohl the cell is composed of the membrane, the primordial utricle, the protoplasm, the nucleus, and the cellular fluid. He arrived at this conception after meticulous studies, which were the first efforts in cytochemistry. An impartial examination makes it appear that Mohl did not go beyond the discoveries of Raspail, which he did not know of and nowhere cites (cf. Klein [1936]).

The history of biology credits Mohl with the invention of the term “protoplasm” (independently of Purkyně, who had already used it in a different sense). A careful reading of the texts reveals that Mohl saw in this substance a preliminary material in cellular generation. This position is all the more surprising because he was one of the first to describe the generation of cells in plants by division starting from preexisting cells. The notion of protoplasm was integrated into the knowledge of the period; but it is a derivative sense of this word, defined by Max Schultze in 1861, which has survived in contemporary biology (cf. Robin [1872] and Klein [1936]). Mohl always limited himself to descriptions of concrete facts and carefully avoided drawing general conclusions from them; moreover, he did not write a synthetic exposition clearly summarizing his stand on the cell theory, which was then in full development.

Mohl had a happy childhood and adolescence, and a university career and personal life without difficulties. He remained unmarried and never attempted to surround himself with a circle of pupils. He was known as a meticulous worker, very clever with his hands, who brought a great number of precise details to bear on very circumscribed problems. He was one of the founders of the Botanische Zeitung (1843), one of the most famous periodicals of modern botany. He was also one of the promoters of the creation of the Faculty of Sciences at Tübingen, the first of its kind in Germany. From the time of his inauguration (1863) he proclaimed his hostility toward speculative thought and, in particular, to German Naturphilosophie, which was then in its dying stages (cf. Bünning [1963]).

Mohl’s great ability was recognized very early in his life. He was awarded many decorations and honorific titles, a fact to which he drew attention. Among numerous academies and learned societies, he was a corresponding member of the Institut de France at a very early age (1838). The Order of the Crown of Württemberg, bestowed in 1843, conferred upon him a title of nobility. He died in his sleep on Easter day 1872. The laudatory obituary of De Bary (1872) and the biography of Sachs (1875) have perpetuated his memory in contemporary biology.


I. Orginal Wokks. Among Mohl’s writings are Mikrographie, oder Anleitung zur Kenntniss und zum Gebrauche des Mikroskops (Tübingen, 1846); “Sur le mouvement du sue à l’intérieur des cellules,” in Annales des sciences naturelles. Botanique, 3rd ser., 6 (1846), 84–96; “Saftbewegung im Inneren der Zellen,” in Botanische Zeitung, 4 (1846), 73–78; 89–94; and “Die vegetabilische Zelle,” in Rudolph Wagner, Handwörterbuchder Physiologie, IV (Brunswick, 1853), 167–309.

II. Secondary Literature. See A. de Bary, “Hugo von Mohl,” in Botanische Zeitung, 30 (1872), 561–579, with complete bibliography; E. Bünning, “Hugo von Mohl (1805 1872),” in H. Freund and A. Berg, Geschichte der Mikroskopie, I (Frankfurt, 1963), 273–280, with portrait; M. Klein, Histoire des origines de la thé cellulaire (Paris, 1936), 60; C. Robin, Anatomie et physiologie cellulaires (Paris, 1873), 7, 249; J. Sachs, Geschichte der Botanik vom 16, Jahrhundert bis 1860 (Munich, 1875), 315–335; and G. Vapereau, Dictionnaire universel des contemporains, 4th ed. (Paris, 1870), 1285–1286.

Marc Klein

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