(b. Wziesko, Silesia, 30 November 1823; d. Berlin, Germany, 6 October 1894)
botany, plant physiology.
Pringsheim belonged to that group of young German botanists—including Ferdinand Cohn, Hofmeister, and Mohl—who revolutionized the science during the middle years of the nineteenth century by shifting attention from collection and taxonomy to the dynamics of cell development and life history. This movement, inspired in large part In Schleiden, created a new appreciation for the degree of unity among all plants and indeed between plants and animals as well. The new insights coincided with, and depended importantly upon, a reexamination of previously neglected organisms. The larger and more familiar flowering plants (phanerogams) increasingly yielded pride of place to the relatively obscure cryptogams, a name long applied to the nonflowering plants because their mode of reproduction seemed hidden.
Hofmeister’s discovery that the higher cryptogams and phanerogams share a common reproductive pattern, in which sexual generation alternates with asexual reproduction, gave special force to the new botanical movement. Pringsheim’s chief contribution to this movement was to identify in the lower cryptogams, and especially in the algae, those basic reproductive modes (notably sexual union and the alternation of generations) that Hofmeister and others had already established for the higher cryptogams.
Pringsheim’s father, the director of an industrial concern, had foreseen a quite different career for his son. During Nathanael’s early education at home and at the Gymnasiums in Oppeln (now Opole) and Breslau (now Wroclaw), his father nourished the hope that he might become an industrialist or merchant. In the face of Pringsheim’s attraction to science, his father urged that he at least direct those interests toward a career in the secure and practical field of medicine. In the winter term of 1843–1844. to meet his father’s wishes, Pringsheim transferred to the medical faculty at the University of Breslau, having already spent several months as a student in the philosophical faculty there. In the spring term of 1844 he moved to the University of Leipzig, also as a medical student. But Pringsheim had never been more than a nominal medical student; and when he moved to the University of Berlin, it was as a declared student of natural science.
At Berlin the professor of botany was Karl Kunth; but Pringsheim’s orientation and approach were more deeply influenced by Purkyně, the exacting physiologist who taught him at Brcslau, and especially by Schleiden’s famous Grundzüge der wissenschaftliche Botanik (1842–1843). In March 1848 Pringsheim very briefly joined the revolutionary movement in Berlin but then withdrew permanently from overt political activity. He took his Ph.D. at Berlin in April 1848. His doctoral thesis defended the controversial view that the cell wall was built up by apposition from the interior and not by adhesion from without. Following additional study in Paris and London, he returned in September 1849 to Berlin, where he became Privatdozent in 1851. Although his Habilitationsschrift, “Die Entwiekelungsgeseluehte der Achlya prolifera” wrongly classified an organism that Pringsheim himself later identified as Saprohgnia ferax (1857), it represented a pioneering attempt to follow the complete developmental history of a lower cryptogam. On 20 May 1851 Pringsheim married Hennelte Guradze, the daughter of a leading merchant in Oppeln. Three daughters were born into this happy union, which lasted more than forty years. Pringshcim’s final months were darkened by his wife’s death in February 1893.
Almost ironically, Pringsheim’s career in pure research benefited immensely from the financial success of his pragmatic father. Upon the latter’s death in 1868, Nathanael inherited an estate in Silesia and Sufficient means to pursue his research freely. In fact, except for his years as Privatdozent at Berlin and a brief period as professor of botany at the University of Jena, Pringsheim held no teaching posts. When called to Jena in 1864 (as Schleiden’s successor), he accepted only after the collapse of preliminary negotiations to secure him a post at Berlin and only on the condition (quickly met) that a new botanical institute be constructed for him at Jena. There Pringsheim lectured in the summer on general botany and in the winter on cryptogams, offering microscopical instruction both semesters.
Despite the gratification of seeing eager students (notably Strasburger) hard at work in his new and well-designed institute, Pringsheim never achieved real happiness at Jena, perhaps because of friction with authorities there, perhaps because he did not really enjoy teaching, but certainly because of increasingly severe attacks of a lung ailment (reportedly asthma) that had troubled him for years and that ultimately caused his death. Pringsheim resigned the post at Jena in 1868 and settled in a house near the botanical gardens in Berlin, where he thereafter conducted his research in a private laboratory attached to his home. Periodic trips to the Riviera and to the northern coast of France brought temporary benefits to his health and permanent additions to his collections of specimens and to his circle of foreign botanical friends.
Pringsheim’s earliest works bore less directly on plant reproduction than on the controversy over Schleiden’s original version of the cell theory. From observations of the vegetative and reproductive cells of many algae, and also of the pollen mother cells of the higher cryptogams and flowering plants, Pringsheim concluded that cell division (and not free-cell formation in a structureless blastema) is the basic mode of cell multiplication. In this conclusion he joined the swelling attack against Schleiden’s “watch-crystal” conception of cell formation. On another front, however, Pringsheim refused to endorse the reformist cause, at least insofar as it was embodied in Mohl’s conception of the “primordial utricle” (Primordial-sehlauch). Mohl claimed that he had seen this peculiar nitrogenous structure surrounding the cell contents but within the cell wall. Insisting that it was a true membrane, he assigned it an important role in cell formation and function and made it part of a wider effort to direct attention away from the cellulose cell wall (so prominent in Schleiden’s scheme) toward the protoplasmic cell contents.
In a monograph of 1854, Pringsheim attacked Mohl’s conception. He argued that Mohl had mistaken a mere layer of the cell contents for a true membrane and emphatically denied Mohl’s claim that cell division took place by the infolding of the primordial utricle, followed by the secretion of a cellulose wall on its outer surface. Instead, Pringsheim insisted that the cell wall arose by direct transformation of the primordial utricle, and that the latter played no active role in cell division, being merely dragged along as a passive lining on the true septa, which were always cellulose. The issues surrounding this debate are extremely complex; and although Mohl’s views more nearly approach the later notion of the cell as a “naked clump of protoplasm with a nucleus,” neither his nor Pringsheim’s position has survived intact. What gives their controversy special interest is the fact that they were observing almost precisely the same cells under almost identical conditions. That they could disagree so fundamentally about what they had seen suggests that their observations were “theory-loaded,” being shaped especially by differing conceptions of cell division.
Pringsheim’s interest in this debate receded somewhat as he made his immediately famous contributions to the discovery of sexuality in the algae. Like most important discoveries in science, this one cannot be assigned to a single worker or to a single moment; it evolved gradually. After Unger, Carl Naegeli, and Hofmeister had provided evidence of sexuality in the higher cryptogams, attention shifted to the previously neglected algae and fungi. Between 1849 and 1851 Thuret, Alexander Braun, and others drew attention to the presence in numerous algae of three different kinds of spores—the familiar resting spores and two types of motile spores that Braun called macrogonidia and nuerogonidia. But no one had yet fully perceived that these spores are sexually differentiated and that the resting spores arise from the sexual union of the two kinds of motile spores. Pringsheim himself had described the germination of resting spores in Achlya [sic Saprolegnia: (1851) and in Spirogyra (1852) without recognizing them as the products of sexual union. In 1854, however, Thuret showed that the resting spores in the brown marine alga Fucus germinate only after the microgonidia (or spermatozoids) attach themselves to the macrogonidia (or egg cell). Moreover, by mixing the spermatozoids from one species with the egg cells from another, he managed to produce hybrids.
Alter confirming Thuret’s results in Fucus and other higher marine algae, Pringsheim turned to lower freshwater species. In 1855 he discovered spermatozoids in the unicellular alga Vaucheria terrestris and carefully described their role in the production of the resting spore: after they attach themselves to the egg mass, a true cell membrane forms on the latter, converting it into a resting spore. Although he also observed a colorless corpuscle inside the egg cell and clearly believed that this corpuscle was a sperm cell, it is an exaggeration to claim (as many do) that he had already observed the actual penetration of the spermatozoids into the egg mass. Until he observed this penetration, many botanists (including Cohn) resisted the startling discovery of so advanced a mode of reproduction in a unicellular plant.
But in this same paper of 1855 Pringsheim had also drawn attention to the wide distribution of differentiated spores in other species, and he now set out to establish his belief that sexual reproduction is a general phenomenon among the algae. Between 1856 and 1858, and in a manner that convinced even the previously skeptical, Pringsheim extended sexuality to the freshwater algae Oedogonium and Coleochaete. In the Oedogonium he definitively observed the actual sexual act, following the spermatozoid as it forced its way through the outer layer of the egg cell and penetrated into its protoplasmic mass, where it dissolved. On this basis he emphasized the crucial point that fertilization involves a real material fusion of the two sexual cells and not (as Thuret had believed) a mere dynamical reaction between them.
Pringsheim’s attempt, during the same period, to establish sexuality in the Saprolegnia (later placed among the fungi) gave rise to an inconclusive debate with Anton de Bary lasting into the 1880’s. De Bary insisted that the family was apogamic and that any sex organs found in it were nonfunctional; Pringsheim maintained that fertilization took place via “spermamoebo” in Saprolegnia with developed anthers. The debate drew interest because of a wider controversy over the existence and origin of sexuality in fungi.
From 1861 to 1863 Pringsheim produced valuable memoirs on the “Water-net” (Hydrodictyon). on Chara (arguing, on the basis of the striking correspondence between its prothallium and the protonema of mosses, that it belonged among the mosses and not the algae, as commonly supposed), and on Salvinia (his most important contribution to our knowledge of ’he higher cryptogams). His inaugural lecture at Jena (1864) emphasized the important place that the cryptogams had come to occupy in the history of botany and general biology. While at Jena, Pringsheim published no papers; but in 1869 he reported his discovery of the conjugation of the swarm spores in Pandorina a process that he viewed as the most primitive form of sexual reproduction. Comparing the anterior ciliated ends where the conjugating spores first united with the “receptive spot” of the ovum in higher algae, the canal cells of archegoniate plants, and the synergidae of angiosperms, Pringsheim insisted upon the embryological unity of the entire plant kingdom.
In 1873 Pringsheim returned to the Sphacelaria, a group of brown marine algae on which he had written a decade before. His main concern now was the bearing of Darwinian evolutionary theory on this family, which displays a progressive complexity from a filamentous to a bulblike structure. Acknowledging that this series supported of the doctrine descent, Pringsheim nevertheless assigned natural selection a minor role. Like many German botanists (including Braun, Cohn, and especially Naegeli), he insisted that the progressive accumulation of structural complexity was a “purely morphological“phenomenon, conferring no survival value, taking place independently of the struggle for existence, and having as its cause an “inherent directing force” (inneren riehenden Kräfte).
Pringshcim’s attempts to extend the law of the alternation of generations to the lower cryptogams excited much controversy. As early as 1856–1858, in his famous papers on alga sexuality, he had introduced the notion that the law might apply in modified form to some species of algae. He showed in particular that the fertilized egg cell in Oedogonium and Coleochaete does not develop directly into a new plant but gives rise instead to a cluster of four asexual spores, each of which becomes a new plant; and he perceived an especially close analogy between the life histories of the Coleochaete and the mosses. Following William Farlow’s observation of 1874 that the asexual phase of the fern could arise directly (that is, vegetatively) from the sexual phase (apogamy), Pringsheim sought to achieve the converse production of the sexual phase directly from the asexual without the intervention of spores (a phenomenon later called apospory). After many experiments he succeeded in producing protonemata (and hence gametes) directly from the divided seta of a moss capsule. This achievement suggested to Pringsheim that plant sexuality was a fluid property, which could be lost or recovered according to circumstances, and that the gametophyte and sporophyte stages should be considered “homologous” since one could give rise to the other vegetatively. On this basis he claimed that the difference between the alternation of generations in the lower cryptogams and that in the mosses and liverworts was one only of degree, with the series of recurrent asexual (sporophyte) generations in the former being reduced to a single such generation in the latter. Put another way, an irregular but homologous alternation of generations in the lower cryptogams gives way to a regular but equally homologous alternation in the mosses and liverworts. In opposition to Pringsheim’s “homologous”’ theory of the alternation of generations, Ladislav Celakovsky proposed his “antithetic” theory’, according to which a regular alternation of generations occurs in the higher cryptogams only through the interpolation of a new, nonhomologous generation (the sporophyte) arising from the division and progressive sterilization of the zygote of a primitive, sexually reproducing plant. Although Pringsheim’s theory had certain advantages from an evolutionary point of view, Celakovsky’s theory was more consonant with some of the histological differences between the lower and higher cryptogams. By the time of Pringsheim’s death, Celakovsky’s theory was the more widely accepted, especially in England, where Bower developed it to a new level of completeness.
Beginning about 1874 Pringsheim turned his attention increasingly to plant physiology, and especially to the function of chlorophyll. In twelve papers extending into the late 1880’s, he developed and defended the remarkable theory that chlorophyll played no direct role in photosynthesis, but rather acted as a protective screen for the plant protoplasm and as a regulator of plant respiration. These functions, he supposed, depended on the capacity of chlorophyll to absorb deleterious and high-energy light rays. His views derived in part from an experimental observation of great significance—namely, that highly concentrated light destroys chlorophyll within a few minutes and plant protoplasm upon prolonged exposure. But he minimized a wide range of alternative explanations for these phenomena, and his startling hypothesis never enjoyed much favor. Nonetheless, it stimulated a flood of work on the subject between 1880 and 1885, including some that established chlorophyll’s role in the absorption of the effective rays in photosynthesis. As part of his theory Pringsheim claimed to have discovered a new substance (“hypochlorin”) that he supposed to he the first product of assimilation and the source of starch and other compounds. His critics argued effectively that hypochlorite if it existed at all, was not an assimilation product but a degradation product of chlorophyll itself. In general Pringsheim’s work in plant physiology did little to enhance, and may have damaged, the reputation built upon his earlier algological work.
In addition to his contributions to research, Pringsheim served botany through his talents for organization and leadership. An advocate of the agricultural benefits of botanical research, he was appointed in 1862 to the Central Commission for Agricultural Experimentation by the Prussian Ministry of Agriculture. In this capacity he submitted four reports over the next decade—on potato growth and the potato blight—based on the work of the Prussian agricultural stations. Pringsheim’s three most important organizational contributions survived him: the Jahrbücher für wissenschaftliche Botanik, which he founded in 1857 and edited until his death; the German Botanical Society, of which he was chief founder in 1882 and president from then until his death: and a biological station that he helped to establish on Helgoland, an algae-rich island in the North Sea off the German coast. After his death, a museum named for him was erected on Helgoland with funds supplied by his children. Pringsheim was elected to the Berlin Academy of Sciences in 1860 and awarded the title of Geheimen Regierungsrat by the Prussian government in 1888.
I. Original Works. Pringsheim’s only book or monograph was Untersuchnngen über den Bau und die Bildung der Pflanzenzeiie, Erste Abtheilung. Grundlinien eincr Theorie der Pflanzcnzelle (Berlin, 1854). A projected second part never appeared. Fifty-seven reports, addresses, and papers (including the monograph above) are collected in Gesammelte Abhandlungen, edited by his children, 4 vols. (Jena, 1895 1896). His major contributions to the discovery of sexuality in the algae appeared initially in three papers in Monatsbcrichte der Königlicher Akademie der Wissenschaften (1855), 133–165; (1856), 225–237; and (1857), 315–330. These papers were subsequently expanded into a four-part treatise published serially between 1857 and 1859 in his own Jahrbücher für wissenschaftliche Botanik, 1 , 1–81, 284–306; 2 , 1–38, 205–236. An epilogue, which seeks to give a critical history of the discovery of algae sexuality, appeared in 1860 (ibid., 2 , 470–481). The fact that the bound volumes of the Jahrbucher sometimes include papers published two or more years before the date of binding, together with the fact that the four-part treatise was an expanded version of three earlier papers, helps to account for the variation in dating some of Pringshein’s contributions.
Among the other papers discussed at some length in the text above are “Über Paarung von Schwärmsporen, die morphologische Grundform der Zeugung im Pflanzenreichc,” in Monatsherichte der Koniglieher Akadenue der Wissenschaften(1869), 721–738; “Ober den Gang der morphologischen Differenzung in der Sphacelarien-Reihe,” in Abhandlungcn der Königlichen Akademie der Wissenschaften (1873), 137–191; and Über Sprossung der Moosfriichte und den Generaiionwcchsel der Thallophyten,” in Jahrbücher für wissenschaftliche Botanik, 11 (1877), 1–46.
For a chronological bibliography of Pringsheim’s works, sec Karl Schumann, Verhattdhmgen der Botanischen Vereins der Provin: Brandenburg, 36 (1894), xl-xlviii. The Royal Society Catalogue of Scientific Papers, V, VIII, XI, XII, and XVII, lists fifty-two papers by Pringsheim (sometimes erroneously paginated) and gives references to English and French abstracts or translations of some of his works. Upon his death, according to Cohn (see below), Pringsheim’s library went to the Berlin botanical gardens, with duplicates sent to the biological station on Helgoland.
II. Secondary Literature. Of the obituary sketches of Pringsheim, the most valuable are Ferdinand Cohn, in Bericht der Deutschen botanischen Gesellschaft, 13 (1895), (10)-(33), repr. inJahrbuch für wissenschaftliche Botanik, 28 (1895), i-xxxii (following p. 321); and D. H. Scott, in Nature, 51 (1895), 399–402. Sec also G. Wunschmann in Allgemeine deutsche Biographie, LIII, 120–124. For an additional list of obituary notices, see the Royal Society Catalogue of Scientific Papers, XVII, 1020.
On Pringshein’s place in the history of botany, see Julius von Sachs, Geschichte der Botanik vom 16. Jahrhundert his 1860 (Munich, 1875), trans, as History of Botany, 1530-1860 by Henry E. F. Garnsey, rev. by Isaac Bayler Balfour (Oxford, 1890), esp. 203, 209–213, 318, 372, 442–443; J. Reynolds Green, A History of Botany, 1860–1900(Oxford, 1909), esp. pp. 47, 51–52, 227, 233, 237, 291–294, 302, 314, 451; and R. J. Harvey-Gibson, Outlines of the History of Botany (London, 1919), esp. 141–144, 161, 170–171, 206–208. For a summary of the controversy over Schleidcn’s cell theory, but without reference to Pringshein’s role, see G. L. Geison, “The Protoplasmic Theory of Life and the Vitalist-Mechanist Debate,” in Isis, 60 (1969), 273–292, esp. 273–278. The controversy is examined at greater length in G. L. Geison, “Toward a Substance of Life: Concepts of Protoplasm, 1835–1870” (M.A. thesis, Yale University, 1967), where Pringshein’s work receives fleeting and somewhat misleading attention.
Gerald L. Geison