Gessner (Gesner), Johannes

(b. Zurich, Switzerland, 18 March 1709; d. Zurich, 6 May 1790)

botany, geology.

Gessner was the son of Christophe Gessner, pastor of the Reformed Church of Zurich for many years, and Esther Maag, a member of a very distinguished Zurich family. For more than four centuries the Gessner family gave Switzerland theologians, physicians, and, above all, naturalists. One of Gessner’s ancestors was Konrad Gesner, whose highly regarded Hitoria animalium earned its author an international reputation. Gesner’s brother Johnan Jakob (1704- 1787) was a well-known theologian who taught Hebrew at the Carolinum and wrote extensively on numismatics.

After receiving a substantial education in Zurich, Gessner went to Leiden to study medicine. Among his teachers there was the famous Dutch physician and botanist Hermann Boerhaave. In Leiden, Gessner also met his fellow Swiss, Albrecht von Haller, and the two became friends. Boerhaave and Haller stimulated his interest in botany, which soon became his favorite area of research. Gessner next went to Paris and then to Basel, where he was initiated into higher mathematics by Johann I Bernoulli. He also became friendly with the latter’s son Daniel, who later introduced probability theory into medicine. Gessner earned his medical degree in 1729, and the following year began to practice in his native city. In 1742 he was in Basel, teaching mathematics. He founded the Société de Physique in 1757 in Zurich, where he remained for the rest of his life.

Accomplished in medicine and physics as well as in botany and mathematics, Gessner was undoubtedly one of the last of the great humanists. He maintained an imposing correspondence with most of the scientists of his time, in particular with Linnaeus. One of the first to adopt the latter’s system of classification, he did much to popularize it.

Gessner established his reputation as a naturalist primarily through his writings in systematic botany. His first important work was Dissertationes de partium vegetationis et fructificationis structura (1743). It was soon followed by Dissertationes physicae de vegetabilibus (1747) and the memoir De Ranunculo bellidifloro et plantis degeneribus (1753), in which he skillfully defended Linnaeus’ conceptions. In De petrificatorum variis originibus praecipuarum telluris mutationem testibus (1756) Gessner showed some recognition of the real nature of fossil plants and in this regard can be considered one of the founders of paleobotany. Moreover, he devoted fourteen years (1759–1773) to the publication of an eleven-part treatise that summarized contemporary knowledge of plants, Phytographia sacra generalis et specialis.

Following Haller’s example, Gessner specialized in the study of Alpine flora. From his very numerous excursions in the Alps and the Forealps he brought back many new species that now bear his name. Gessner was an innovator in his botanizing, since he was quite probably the first to describe plant habitats; for example, he provided altimetric data obtained with the aid of a barometer.

Toward the end of his life Gessner concentrated on geological observations. He was interested in the formation of mountain chains on the European continent and estimated the era and duration of their formation with great care. Gessner’s research led him to attack the brief chronologies—based mainly on theological considerations—that were generally accepted at the time. A brilliant advocate of the principle of geochronological extrapolation, his work foreshadowed modern geophysics. Finally, his extremely precise observations of the mineral springs of the Alps were long authoritative.

The recipient of many honors, a member of countless scientific societies, and a correspondent of most of the European academies, Gessner was, in his own lifetime, considered one of the greatest naturalists of the age. Yet, shortly after his death he was somewhat forgotten, and new plants that he had been the first to describe were attributed, often wrongly, to his illustrious ancestor Konrad Gesner. He was also confused with Johann Matthias Gessner, a German pedagogue, humanist, and botanist, whose books were widely distributed. In addition, Gessner’s memoirs on Alpine flora in particular could hardly withstand the inevitable comparison with those of Haller. It is only very recently, notably with the publication in 1949 of Gessner’s correspondence with Linnaeus, that his originality and importance have finally gained recognition.

BIBLIOGRAPHY

I. Original Works. Gessner’s works are Dissertationes de partium vegetationis et fructificationis structura (Zurich, 1743); Dissertationes physicae de vegetabilibus (Zurich, 1747); De Ranunculo bellidifloro et plantis degeneribus (Zurich, 1753); De petrificatorum varies originibus praecipuarum telluris mutationem testibus (Zurich, 1756); Phytographia sacra generalis et specialis (Zurich, 1759–1773); and Tabulae phytographica analysin generum plantarum exhibentes, with commentary and edited by C. S. Schinz (Zurich, 1795–1826).

II. Secondary Literature. On Gessner’s life and work, see G. R. de Beer, “The Correspondence Between Linnaeus and Johannes Gessner,” in Proceedings of the Linnean Society of London, 161 (1948–1949), 225; H. K. Hirzel, Denkrede auf Johannes Gessner (Zurich, 1790); and Rudolf Wolf Biographien zur Kulturgeschichte der Schweiz, I (Zurich, 1858), 281–322.

P. E. Pilet