Naegeli, Carl Wilhelm on
NAEGELI, CARL WILHELM ON
(b. Kilchberg, near Zurich, Switzerland, 27 March 1817; d. Munich, Germany, 10 May 1891)
The son of a physician, Naegeli was educated at a private school, the Zurich Gymnasium, and Zurich University. His enthusiasm for science was stimulated by Oken’s lectures on zoology, and in 1839 he gave up medicine at Zurich to study botany under Alphonse de Candolle at Geneva. In 1840 he received the doctorate for his study of Swiss Circia, a work marked by the same precision and detail as his later studies. There followed a summer semester in Berlin when he studied Hegel’s philosophy. Hegel had been dead eleven years, but his writings were still much admired. Although in retrospect Naegeli claimed that he had found nothing useful in Hegelianism, his work is characterized by a Hegelian search for universal concepts which at times seems pedantic and misdirected.
In the autumn of 1842 Naegeli left Berlin for Jena, where he worked with Schleiden. Together they published the new, and short-lived, journal Zeitschrift für wissenschaftliche Botanik. Naegeli’s eighteen months in Jena were highly productive. From 1845 to 1852 he worked in Zurich, first as Privatdozent, then as assistant professor. There his collaboration with Carl Cramer in plant physiology research began in 1850. This work was continued when he became full professor at Freiburg im Breisgau in 1852. Finally in 1857 he accepted the chair of botany in the University of Munich. There, in 1890, he celebrated the fiftieth anniversary of his degree.
When Naegeli arrived in Jena, Schleiden had just published his famous Grundzüge der wissenschaftlichen Botanik, which begins with a lengthy critique of the philosophY of science and goes on to enunciate the Schleiden-Schwann theory of free cell formation, the analogy of cryptogamous spores with phanerogamous pollen, and the assertion that the embryo in phanerogams is the transformed tip of the pollen tube. Like Schleiden, Naegeli began with a philosophical essay, “Über die gegenwärtige Aufgabe der Natur-gesehichte, insbesondere der Botanik,”in which he eschewed compilations of empirical data, since science is concerned not with the changing characteristics of individuals but with the unchanging laws relevant to all individuals. When he sought to practice science in harmony with this definition he ran into difficulties. His early studies of cell division (1844, 1846) appeared to show two types of cell formation—free cell forma- tion and division of preexisting cells. At first he found the latter process in all cells of algae and diatoms and in all spore mother and pollen mother cells of lower and higher plants. Two years later he altered this decision, making a simple distinction between reproductive tissues, in which free cell formation rules, and vegetative tissues, in which cell division rules. Meanwhile a more decisive stand in favor of cell division had been taken by Unger.
These studies of cell formation illustrate Naegeli’s striving for general laws, the strong influence of Schleiden on him, and his eye for detail. Thus he realized that in cell division the wall formed between the two daughter cells is the result, not the cause, of cell division. The latter he recognized as the function of the whole protoplast. These studies also gave valuable support to Robert Brown’s assertion of the invariable presence of a single nucleus in every cell, and it is to his and Mohl’s credit that the protoplasmic lining of the cell (Naegeli’s Schleimschicht) was recognized as the living substance.
Naegeli’s failure in 1846 to limit correctly the application of Schleidein’s theory of cell formation must be balanced against his brilliant achievement in 1845, when he studied apical growth. This work culminated thirteen years later in his researches into the formation of tissues in the stems and roots of vascular plants, which constituted a major contri- bution to plant anatomy. For his study of apical growth he began with simple cases—from the Bryophyta—and in his thorough manner he traced back the various tissues and organs in a cell lineage to the apical cell. The regular way in which this cell cuts off daughter cells in either one, two, or three rows gave Naegeli an example of the operation of laws which he could represent mathematically and which for him pointed the way to absolute concepts of the sort characteristic of science proper. It was no accident that he used the phrase wissenschaftliche Botanik in the title of two of his series of papers, nor was it uncharacteristic for him to represent apical cell division in terms of equations. This was the realization of Schleiden’s theory that the development of plants would one day be expressed by mathematical laws. Naegeli’s success in thus tracing cell lineages had a profound impact on the botanists of his time.
Extending these studies to the vascular cryptogams and the angiosperms, Naegeli arrived at the important distinction between formative tissues (Bildungsgewebe), which he divided into cambia and meristems, and structural tissues (Dauergewebe) no longer actively multiplying. In the stems and roots of plants was a strain of cells (cambial and meristematic) which remained untouched by differentiation and whose origin could be traced back to the original “foundation cell”or zygote. Unfortunately he did not draw the same conclusion from these findings as did Weismann from his study of the Coelenterata. Naegeli’s conception of an hereditary and a nutritive component in every cell derived instead from the facts of sexual reproduction.
In 1844 Naegeli discovered the antherozoids of ferns and in 1850 those of the Rhizocarps. He also discov- ered the protonema and archegonia in Ricciocarpus, but it was left for Hofmeister to arrive at the correct analogies between these organs and those of the phanerogams. It seems that Naegeli was too much under Schleiden’s influence. How else could he have rejected the discovery of antherozoids in Fucus by Decaisne and Thuret in 1849?
Naegeli made a major contribution to the field of cell ultrastructure when he published his detailed study of starch grains in 1858. Here he arrived at his micellar theory, according to which such amorphous substances as starch and cellulose consist of building blocks, which he later termed “micelles,”packed in crystalline array. Each micelle was an aggregate of up to nine thousand molecules (“atoms”in Naegeli’s terminology) of starch. Water could penetrate between the micelles, and new micelles could form in the interstices between old micelles. The swelling property of starch grains and their growth by intussusception were thus based on a molecular-aggregate model, which he also applied to the cellulose of the cell wall. Three years later (1861) he reported on the anisotropy of starch grains and of cell walls from observations with the polarimeter, which he took as supporting his assumption of crystalline ultrastructure. Other botanists, notably Strasburger, put a different inter- pretation upon this anisotropy.
Nevertheless, Naegeli’s micellar theory stimulated studies of ultrastructure and initiated a tradition of the study of botanical ultrastructure in Germany and Switzerland, a tradition continued by Hermann Ambronn in Jena and Alfred Frey-Wyssling at the Polytechnic in Zurich. Naegeli’s work also fostered a belief in micellar aggregates at the expense of the macromolecular concept; a lengthy debate ensued in the 1920’s and 1930’s between the concept of a long chain polymer and an aggregate or micell of several shorter chains.
In his search for general laws, Naegeli used his micellar theory, which was based on carbohydrate products, to arrive at a molecular-aggregate model of the hereditary substance, its expression, growth, and modification. This inspired piece of deductive thinking appeared in his famous Mechanisch-physiologische Theorie der Abstammungslehre (1884), where the important distinction is made between the nutritive trophoplasm and the hereditary idioplasm—the egg being rich in trophoplasm, the spermatozoon almost completely without it. Since paternal and maternal characteristics are transmitted approximately equally, they must be carried by the idioplasm and not by the trophoplasm. Other biologists, notably Weismann and Nussbaum, developed this idea in relation to current work in cytology. Whereas Naegeli made his idioplasm a continuous web of fibers which penetrated cell walls, Weismann limited it to the chromosomes in each cell. Oscar Hertwig, on the other hand, who was much influenced by Naegeli, did not restrict the idioplasm to the chromosomes but to the nuclear substance as a whole.
Naegeli’s micellar theory can be seen as the fulfillment of his aim to put Schwann’s crystal model of cell growth on a sound footing. The studies he published on the cell wall of Caulerpa in 1844 mark the beginning of this work which culminated in his grand synthesis of 1884.
Despite Naegeli’s creation of molecular models, he never made a complete break with the vitalistic and teleological ideas so popular among German-speaking biologists of his youth. Consequently natural selection was for him only a pruning device, evolution being the result of an internal perfecting principle. To the end of his days he believed in the spontaneous generation of cells and that, in view of the time required for com- plexity to be achieved, simple organisms must be younger than complex ones. His search for dis- continuities between species and between the plant and animal kingdoms was consistent with his desire for absolute concepts. It was to Naegeli—who had denied the existence of antherozoa in Fucus, of genuine species of microorganisms responsible for infectious diseases, and of Darwin’s role for natural selection—that Gregor Mendel sent his “Versuche über Pflanzehybriden.” Naegeli, who believed he himself knew how hybrids behaved from his study of crosses in the genus Hieracium, regarded Mendel’s hybrid ratios and demonstration of complete reversion as of purely empirical significance, irrelevant to genuine species.
As one of the nineteenth century’s foremost botanists and influential theoreticians, Naegeli deserves sympathetic evaluation as both an innovator and a victim of the biological thinking to which he contributed so much. Where he failed so conspicuously his famous pupil Carl Correns succeeded. Correns was one of the three rediscoverers of Mendel’s laws.
I. Original Works. A complete list of Naegeli’s publications will be found in S. Schwendener’s obituary notice (see below). With Schwendener he wrote the very popular Das Mikroskop; Theorie und Anwendung desselben,
2 vols. (Leipzig, 1867), English trans, by F. Crisp (London, 1887; 2nd ed., London, 1892). Naegeli introduced the term Micell in the 2nd German ed. of 1877. With A. Peters he wrote Die Hieracien Mittel Europas. Monographische Bear- beitung der Piloselloiden mit besonderer Berücksichtigung der mitteleuropaischen Sippen, 2 vols. (Munich, 1885– 1889). Naegeli’s final statements on heredity, growth, and ultrastructure will be found in Mechanisch-physiologische Theorie der Abstammungslehre (Munich Leipzig, 1884).
The majority of his earlier cytological papers appeared in the short-lived journal which he and Schleiden edited, Zeitschrift für wissenschaftliche Botanik (Jena, 1844–1847). The most important papers from this journal were trans- lated into English by Arthur Henfrey and published in the Ray Society’s Reports and Papers on Botany (London, 1846,1849). Naegeli’s studies of starch grains, his micellar theory, and his work with C. Cramer were published in the series Pflanzenphysioiogische Untersunchungen von C. Naegeli und C. Cramer, nos. 1–4 (Zurich, 1855–1858). A selection from Naegeli’s contributions was published by Albert Frey in Die Micellartheorie … Auszüge aus den grundlegenden Originalarbiten Nägelis, Zusammenfassung und kurze Geschichte der Micellartheorie, in Ostwald’s Klassiker der exakten Wissenschaften, no, 227 (Leipzig, 1908).
Forty-two papers presented by Naegeli to the Bavarian Academy are in Botanische Mitteilungen aus den Sitzungs- berichten der k. b. Akademie der Wissenschaft in München, III (Munich, 1863 1881). Extracts from Naegeli’s letters to Mendel were published by Hugo lltis in his Life of Mendel (London, 1932; repr. 1966).
II. Secondary Literature. A long list of obituary notices is given in the Royal Society Catalogue of Scientific Papers, 17 (1891), 443. Readily available is D. H. Scott’s notice in Nature, 44 (1891), 580–583.
The only biographical notice which includes a full biblio- graphy is that by S. Schwendener in Bericht der deutschen botanischen Gesellschaft, 9 (1891), (26)-(42). Most accounts of Naegeli’s life rely on C. Cramer, Leben und Wirken von Carl Wilhelm Nägeli (Zurich, 1896; first published in the Neue Zürcher Zeitung, 16 May 1891). For a critical account of Naegeli’s botanical work see Sidney Vines’s obituary notice in the Proceedings of the Royal Society, 51 (1892), 27–36. The work of Naegeli and Schwendener is included in A. Frey-Wyssling’s paper, “Frühgeschichte und Ergebnisse der submikroskopischen Morphologie,”in Mikroskopie, 19 19 , 2–12. Naegeli’s micellar theory has been analyzed in depth by J. S. Wilkie. His summary of this work appeared in Nature, 209 (1961), 1145–1150, and his detailed papers are “Nageli’sm Work on the Fine Structure of Living Matter,”nos. I, II, IIIa, in Annals of Science. 16 (1960), 11–42, 171–207, 209–239, and ibid., 17 (1961), 27–62.
Naegeli’s philosophical position and his attitude to Mendel are discussed in J. S. Wilkie’s commentary to the paper by Bentley Glass, “The Establishment of Modern Genetical Theory as an Example of the Interaction of Different Models, Techniques, and Inferences,”in A. C. Crombie, ed., Sentific Change, Symposium on the History of Science…Oxford (London, 1963), 521–541, commentary on 597–603. Naegeli’s attitude to Mendel has also been discussed by A. Weinstein, “The Reception of Mendel’s Paper by His Contemporaries,”in Proceedings of the Tenth International Congress of the History of Science (Ithaca, 1962; Paris, 1964), 997–1001, and in R. C. Olby and P. Gautrey, “Eleven References to Mendel Before 1900,”in Annals of Science, 24 (1968), 7–20. C. C. Gillispie has compared the speculative ideas of Naegeli and Weismann in The Edge of Objectivity: An Essay in the History of Scientific Ideas (Princeton-London, 1960), 322–328.