(b. Mont-sous-Vaudrey [Jura], France, 13 April 1852; d. Paris, France, 7 March 1928)
After completing his preliminary education in Mont-sous-Vaudrey, where his parents earned a livelihood by farming, Guignard went on to receive his secondary school diploma (baccalauéat ès letters) in Besançon. From 1871 to 1874 he worked as an apprentice in several pharmacies in Paris. Then in 1874 he enrolled in the Paris School of Pharmacy and concurrently pursued studies at the Faculty of Sciences. Guignard also competed successfully for an appointment to an internship in pharmacy in the Paris municipal hospitals where he served with distinction from 1876 to 1882.
From this formative period, Guignard emerged in 1882 with an advanced qualification in pharmacy (diplôme supérieure) and a doctorate in natural sciences from the Faculty of Sciences. Two outstanding theses crowned his scholastic achievement: a study of the embryo sac in angiosperms for this diplôme supérieure) in pharmacy and a brilliant investigation of the embryogeny in leguminous plants for his docteur ès sciences naturelles. Both works immediately established him as a botanist of considerable ability.
His student years behind him, Guignard worked briefly as an assistant and aide-naturalist at the Museum of Natural History. In 1883 he left for Lyons where he became professor of botany at the Faculty of Sciences and director of the botanical garden of that city. Appointed professor of botany at the Paris School of Pharmacy in 1887, he served in that capacity until 1927 and was also director of the school from 1900 to 1910. Guignard was elected to many learned societies including the Botanical Society of France (president, 1894); the Paris Academy of Medicine; Academy of Sciences (president, 1919); Society of Biology (vice-president, 1894); and the National Society of Agriculture of France.
Guignard’s publications dating from 1880 represented more than four decades of botanical investigation. His most important contributions were to embryology, cytology, fertilization, the morphology and development of the seed, and his study of reproductive organs in plants. Of considerable interest too was his research on the sites of specific plant principles, organs of secretion, and his work in bacteriology.
In 1882 Guignard demonstrated that the embryo sac in flowering plants always develops from one of the hypodermal cells of the nucellus and described the general character of the eight-nucleate embryo sac in thirty-six families of monocotyledons and dicotyledons. Shortly after, in 1883, Guignard observed the longitudinal division of chromosomes in karyokinesis, thus confirming W. Fleming’s findings. But even more important was his confirmation in 1889 of meiosis in plants, a phenomenon discovered a year earlier by E. Strasburger.
Double fertilization in angiosperms was discovered by Guignard in 1899 independently of S. Nawaschin, who had announced his discovery of the same phenomenon at a scientific meeting in Kiev, Russia, in 1898. In the meantime, Guignard had expanded the scope of his work to include such studies as the morphology of bacteria; pollen formation; the role of the centrosome and related bodies; the development and structure of the male gamete in Fucus, liverworts, mosses and ferns; the localization of hydrocyanic acid, glycosides and enzymes in plants; the growth and development of the seed, especially the tegmen, and investigations of organs of secretion in Laminaria and Copaifera.
From 1900 to 1922, Guignard continued his research on fertilization, embryogeny, and pollen formation, while devoting a major portion of his time to studying the sites of production in plants of sulfurated and cyanogenetic glycosides and their enzymes. His findings, published in 1906, on the poisonous nature of the Java bean (Phaseolus lunatus L). showed that the toxicity was due to its hydrocyanic content and led to a ban on the importation of the bean into France. Guignard also developed a sensitive test for determining hydrocyanic acid in plants by means of sodium picrate paper. Grafting experiments with cyanogenetic plants convinced Guignard that, except when two species of the same genus were grafted, there was no migration of cyanogenetic glycosides between graft and stock; each retained, in this respect, chemical autonomy.
After 1907 there was a marked decline in the number of Guignard’s scientific publications. His most significant scientific accomplishments had been made by the turn of the century, and his work on the localization of plant principles had brought him to the threshold of a new field of inquiry, the study of plant biosynthesis.
I. Original Works. For a comprehensive listing of Guignard’s publications, see P. Guérin, “Léon Guignard, 1852–1928,” in Bulletin des sciences pharmacologiques, 35 (1928), 374–380.
II. Secondary Literture. The fullest account of Guignard’s life and work will be found in P. Guérin, cited above, pp. 354–380. See also R. Souèges, “Léon Guignard,” in Figures pharmaceutiques françaises (Paris, 1953), pp. 203–208. A good discussion of Guignard’s contributions to plant embryology is included in R. Souèges, L’embryologie végétale, résumé historique, 2 vols., II (Paris, 1934), 19–21 and passim
For Guignard’s work in cytology, see Maurice Hocquette, “Morphologie, anatomie, cytology,” in A. Davy de Virville, et al., Histoire de la Botanique en France (Paris, 1954), pp. 147–149, 151; and A. Hughes, A History of Cytology (London-New York, 1959), pp. 66, 70–72.