Correns, Carl Franz Joseph Erich

(b. Munich, Germany, 19 September 1864; d. Berlin, Germany, 14 February 1933),

botany, plant genetics.

Correns was the only child of Erich Correns, a painter and member of the Bavarian Academy of Art. His mother was of Swiss extraction.

Orphaned at seventeen Carl left Munich for St. Gall, Switzerland, where tuberculosis interrupted his schooling and prevented him from obtaining his Abitur until 1885. Four years later he graduated from the University of Munich; and after two semesters in Berlin under Schwendener he moved to Tübingen, where he took his Habilitation in 1892. In the same year, he married Elizabeth Widmer, a niece of Karl von Naegeli, After ten years as Privatdozent, Correns was appointed assistant professor at Münster in 1909. When the Kaiser-Wilhelm Institut für Biologie was built in Berlin (Dahlem) in 1913, Correns became its first director. There he remained for the rest of his life, and his unpublished manuscripts were preserved there until their destruction during the bombing of Berlin in 1945.

Correns won fame as a rediscoverer of Mendel’s laws. Whereas de Vries and Tschermak, who rediscovered Mendel’s work simultanteously, were more concerned with mutation and practical plant breeding, respectively, Correns concentrated on the xenia question: Does foreign pollen have a direct influence on the characteristics of the fruit and seed? This subject was but one of many botanical problems occupying his attention in the 1890’s. Correns had studied under Karl von Naegeli; and his study of cell wall growth, which formed the subject of his Habilitationsschrift, was devoted to an attack on E. Strasburger’s theory of growth by apposition and a defense of Naegeli’s intussusception theory. Other subjects that he studied at this time were the floral morphology of Dioscorea, Primula vulgaris, Aristolochia, Calceolaria, and Salvia; the physiology of plant sensitivity in Drosera and climbing plants; the initiation of leaf primordia; and vegetative reproduction in mosses and liverworts.

The many-sided character of Correns’ early research indicates the indecision of one trained in the shadow of giants, Naegeli and Darwin in particular. His work represents a reinvestigation, extension, or criticism of previous work. He studied heterostylism in the primrose because of disbelief in Darwin’s and G. G. F. Delpino’s views on adaptation to outbreeding. Following his mentor Naegeli, he denied that the large and small pollen grains are an adaptation to long-and short-styled flowers because culture of the grains in a sugar solution failed to yield the required difference in length. In his study of Drosera rotundifolia Correns also questioned Darwin’s conclusions on the effect of increasing temperature on the sensitivity of leaves.

In 1894 Correns took up the xenia question, studying it by crossing varieties of Zea, Pisum, Phaseolus, Lilium, and Matthiola. Three years later he concluded that the xenia effect in maize is due either to an enzymatic effect of the embryo on the endosperm tissue or to a genuine hybridization between the secondary embryo sac nucleus and a generative nucleus of the pollen tube. (Mistakenly, he was thinking of a division of the nucleus, which serves as gamete to the egg cell, to form two nuclei, one for the egg cell and one for the endosperm.) While Correns delayed seeking cytological prooof, S. G. Nawaschin and L. Guinard showed that it Lilium one of the original generative nuclei of the pollen tube fuses with the endosperm nucleus. Correns did not learn of this until late in 1899. Meanwhile, his pea crosses had reached the fourth generation. Here the color change, unlike that in maize, presented no problem to Correns, who, like Mendel, realized that only the cotyledons of the new embryo—not the mother tissue—were involved. His scoring of maize progeny had given him complicated numerical results, but his pea progeny gave him simple ratios; and in October 1899 Correns arrived at the correct explanation. A few weeks later he read Mendel’s paper, of which he had learned from a rereading of W. O. Focke’s Die Pflanzenmischlinge. On 21 April Correns was stimulated to write up his own account by the receipt of de Vries’s paper “Sur la loi de disjonction des hybrides,” The German Botanical Society received it on 24 April.

Of the three rediscoverers of Mendel’s laws, Correns showed the deepest understanding and the most subtle approach. The remainder of his career was devoted to an investigation of the precise extent of the validity of these laws. He was the first to correlate Mendelian segregation with reduction division and to show that Mendelian segregation does not require the dominant-recessive relationship, and that characters, even those due to different physiological agents, can be “coupled” or “conjugated” in heredity and are therefore unable to show independent assortment (Mendel’s second law). In 1902 he found in maize a case of coupling between self-sterility and blue coloration of the aleurone layer; here too he found the first evidence of differential fertilization between different gametes. This finding was later supported by his discovery of competition between male and female pollen grains, the former having a selective advantage over the latter. In the same year as Walter Sutton (1902), Correns produced a chromosome theory of heredity that allowed for exchange of genes between homologous chromosomes but not for the block transfer type later advanced by Morgan. On Correns’ scheme, therefore, mapping of the genes from crossover values would be impossible.

In 1903 Correns predicted that sex is inherited in a Mendelian fashion, and in 1907 he proved it by his classic experiments with Bryonia. Two years later he obtained the first proof of cytoplasmic inheritance in plants simultaneously and independently of Erwin Baur. From that year until his death Correns studied plant variegation in all its forms, and by crossbreeding experiments he distinguished between nuclear, Mendelian and extranuclear, non-Mendelian inheritance of variegation. Whereas Baur proposed that the plastids themselves are the genetic determinants (Plastom theory) in cases of extranuclear heredity, Correns favored the nonparticulate cytoplasm of the cell considered as a whole (non-Plastom theory). For Baur the change from green to white cells was due to plastid mutation; for Correns in 1909 it was a case of disease, but in 1922 he postulated a labile state of the cytoplasm that could cause the plastids to develop either into normal (green) bodies or into diseased (white) bodies. Although the Plastom theory is now widely accepted both for biparental and for monoparental cytoplasmic inheritance, in Correns’ time the failure to detect cell with white and green plastids mixed and to see a clear boundary between mutant and normal tissues seemed to furnish valid objections to Baur’s theory.

Correns was unimpressive as a lecturer. He always published in German and rarely traveled. Unlike de Vries, who forced the facts of heredity into an oversimplified Mendelian scheme, Correns stressed the complexities and the exceptions to that scheme. Unfortunately his efforts to introduce more precise terminology were clumsy and did not win acceptance. Yet in 1900 his view of heredity had a sophistication and depth that geneticists in general would not achieve for nearly two decades. He was a hard worker, dedicated to science rather than to success, and willingly gave Mendel full credit, later publishing Mendel’s famous letters to Naegeli. He deserves the first place in the history of the rediscovery period of Mendelian genetics.

BIBLIOGRAPHY

1.Original Works, Nearly all of Correns’ 102 papers were reprinted in his Gesammelte Abhandlungen zur Vererbungswissenschaft aus periodischen Schriften 1899—1924, F. von Wettstein, ed. (Berlin, 1924). A complete list up to 1923 will be found in Sierp’s paper (see below). Although he published no books, Correns did contribute two lengthy monographs to the series Handbuch der Vererbungswissenschaft: “Bestimmung, Vererbung and Verteilung des Geschlechtes bei den hoheren Pflanzen,” 2c (1928), 1–138; and “Nicht mendelnde Vererbung,” F. von Wettstein, ed., 2h (1937).

Corrber das Verhalten der Nachkommenschaft der Rassenbastarde,” in Bericht der Deutschen botanischen Gesellschaft, 18 (1900), 158–167, is available in translation in C. Stern and E.R. Sherwood, eds., The Origin of Genetics. A Mendel Sourcebook (San Francisco-London, 1966) pp. 119–132. Little-known but excellent is Correns’ retrospective essay “Die ersten zwanzig Jahre Mendelscher Vererbungslehre,” in Festschrift der Kaiser-Wilhelm Gesellschaft. Forderung der Wissenschaft (Berlin, 1921), pp. 42–49.

II. Secondary Literature. Obituary notices appeared in Nature, 131 (1933), 537–538; and Naturwissenschaften, 22 (1933), 1–8, with foreword by Max Planck and portrait. Two accounts of Correns’ work which complement each other are E. Stein, “Dem Gedächtnis von Carl Erich Correns nach einem halben Jahrhundert der Vererbungswissenchaft,” in Naturwissenschaften, 37 (1950), 457–463; and H. Sierp, “Die nichtvererbungswissenschaftlichen Arbeiten von Correns,” Ibid., 12 (1924), 772–780. In the same volume there is a photograpth of Correns,” pp. a paper by A. Zimmermann, “Carl Erich Correns,” pp. 751–752. For a modern assessment of Correns’ work on plastid inheritance see R. Hagemann, Plasmatische Vererbung (Jena, 1964); and J. T. O. Kirk and R. A. E. TilneyBassett, The Plastids. Their Chemistry, Structure, Growth and Inheritance (London-San Francisco, 1967).