THURET, GUSTAVE ADOLPHE

(b. Paris, France, 23 May 1817: d. Nice, France, 19 May 1875)

botany.

The third son of Isaac Thuret, consul general of the Netherlands in France, and Jacoba Henrietta van der Paedevoort, Thuret belonged to a French Protestant family that had emigrated to Holland following Louis XIV’s revocation of the Edict of Nantes. He received a religious education and remained a strong Protestant. After being tutored in the classics, he studied law at Paris, and obtained the licence in 1838. During his youth he made many trips abroad, especially to England; and he spoke English fluently, having been taught it by his mother before he learned French.

Named attaché to the French embassy in Constantinople in 1840, Thuret soon gave up a diplomatic career to devote himself to botanical research. A very wealthy man, he remained an amateur, never seeking a university post. Nevertheless, the importance of his discoveries brought him a corresponding membership in the Academic des Sciences in 1857.

In order to further his research. Thuret hired an assistant–a medical student, Edouard Bornet (1828-1911) who soon became his collaborator and friend. While studying marine algae at Cherbourg. Thuret also drew on the services of the artist A. Riocreux, who skillfully reproduced Thuret’s microscopical observations. The latter commenced in 1840 with the discovery of the flagella of the spermatozoids among the Characeae. This encouraged Thuret to look for similar locomotive organs among the other cryptogams, particularly the algae.

Working with Joseph Decaisne, Thuret attempted to study live Fucus, obtained from fish markets in Paris. They soon realized, however, that such observations could be made only at the seashore, where much more active live algae were available, along with seawater in which to observe them. Upon their return from a trip to the coast of Normandy, Decaisne and Thuret announced the discovery of the spermatozoids of Fucus to the Académie des Sciences on 11 November 1844. They described a red granule (stigma) and two unequal flagella, one pointing forward and the other backward. The subtlety and precision of their observations is remarkable, especially considering the imperfect state of the microscopes at their disposal.

The Académie des Sciences proposed the following subject for the grand prize in the physical sciences for 1847: “L’étude des mouvements des corps reproducteurs ou spores des Algues zoosporées et des corps renfermés dans les anthéridies des Cryptogames.” The prize was shared by the two papers submitted, one by Thuret and the other by two naturalists from Marseilles, A. Derbes and A. J. J. Solier. Thuret’s paper, however, was incontestably superior. Basing his analysis on the color of the zoospores and of the spermatozoids, as well as on the mode of insertion and orientation of the flagella, Thuret established, among the Zoosporeae classified by Decaisne, a very sharp distinction between the green algae (Chlorosporeae) and the brown algae (Phaeosporeae).

In 1852 Thuret left Paris and moved to Cherbourg, where he completed his initial investigation of Fucus. Through skillful fertilization experiments, in the course of which hybrid zygotes were obtained, he demonstrated the role of the spermatozoids in fertilization. Thus in 1854 he clarified the crucial phenomenon of fertilization, which had been shrouded in mystery. He was, however, unable to bring about the fusion of the male and female gametes, observed shortly afterward in another alga (Oedogonium) by Nathanael Pringsheim.

Thuret had verified the existence of spermatozoids and of mobile zoospores among green and brown algae, but the reproduction of the blue and red algae remained unknown, since no flagellated cell had been observed in either group. Thuret soon established, however, the absence of sexual reproduction among the blue algae, which multiply only by spores or by fragmentation of the trichomes into hormogonia. The problem of reproduction among the red algae appeared more intractable until 1866, when Thuret and Bornet ascertained that the male gametes (pollinia or spermatia), which never move, cling to and fuse with the hair (trichogyne) surmounting the female cell. They thereby discovered the wholly unexpected fertilization process that precedes the development of the carpospores. The formation of the carpospores, moreover, is accompanied by fusion phenomena that are often complex, involving the mother plant (auxiliary cells). Through the discoveries of Thuret and Bornet, the extremely varied reproductive modes of the different groups of algae, virtually unknown twenty-five years earlier, were definitively elucidated, at least in broad outline.

Thuret confirmed his discoveries by observations of a large number of species. In order to publicize them, he began two books, both of which were completed after his death by Bornet: Notes algologiques (1876–1880) and Études phycologiques (1878). They were illustrated with remarkable copperplate engravings of Riocreux’s drawings that combined scientific exactitude with artistic beauty.

Thuret found it difficult to live in the humid climate of Cherbourg, and in 1856 he moved to the Mediterranean coast at Cap d’Antibes, which was then almost uninhabited. There he bought two fields and built a large villa where he continued his research on Mediterranean algae. His reputation attracted to Antibes a number of foreign botanists who wished to study algae: W. G. Farlow, E. de Janczewski, M. Woronin, and J. Rostafinski, among others. Thuret transformed the land surrounding the villa into a splendid botanical garden into which he introduced many exotic ornamental plants, which are now common in all the gardens along the Côte d’Azur. The “Villa Thuret”, which its founder bequeathed to the nation, is now an agronomic research station. Thuret left his algologic collections and library to Bornet, who in turn gave them to the Muséum d’Histoire Naturelle in Paris.

The outstanding characteristic of Thuret’s research was his constant concern to observe fully alive algae in their natural environment. This grasp of the necessity for working under conditions that permit the subject of study to remain alive was still unusual in Thuret’s time, as was his broad biological conception of the methods suitable for the study of development and of the role of the reproductive organs. Together, these advanced views enabled Thuret to make a wealth of discoveries that revealed the extreme diversity in the reproductive modes of the algae and opened the way for further progress in the subject.

BIBLIOGRAPHY

An obituary is E. Bornet, “Notice biographique sur M. Gustave-Adolphe Thuret”, in Annales des sciences naturelles, 6th ser., Botanique, 2 (1875), 308–361, and in Mémoires de la Société impériale des sciences naturelles de Cherbourg, 20 (1876).

Jean Feldmann