# 1911 Encyclopædia Britannica/Naegeli, Karl Wilhelm von

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​NAEGELI, KARL WILHELM VON (1817–1891), Swiss botanist, was born on the 27th of March 1817 near Zurich. He studied botany under A. P. de Candolle at Geneva, and graduated with a botanical thesis at Zurich in 1840. His attention having been directed by M. J. Schleiden, then professor of botany at Jena, to the microscopical study of plants, he engaged more particularly in that branch of research. Soon after graduation he became Privat dozent and subsequently professor extraordinary, in the university of Zurich; in 1852 he was called to fill the chair of botany in the university of Freiburg-in-Breisgau; and in 1857 he was promoted to Munich, where he remained as professor until his death on the 11th of May 1891. Among his more important contributions to science were a series of papers in the Zeitschrift für wissenschaftliche Botanik (1844–1846); Die neuern Algensysteme (1847); Gattungen einzelliger Algen (1849); Pflanzenphysiologische Untersuchungen (1855–1858), with C. E. Cramer; Beiträge zur wissenschaftlichen Botanik (1858–1868); a number of papers contributed to the Royal Bavarian Academy of Sciences, forming three volumes of Botanische Mitteilungen (1861–1881); and, finally, his volume, Mechanisch-physiologische Theorie der Abstammungslehre, published in 1884.
The more striking of his many and varied discoveries are embodied in the Zeitsch. für wiss. Bot. In this we begin with Naegeli’s extension of Robert Brown’s discovery of the nucleus to the principal families of Cryptogams, and the assertion of its universal occurrence in plants, together with the recognition of its vesicular structure. There is further his investigation of the “mucous layer” (Schleimschicht) lining the wall of all normal cells, where he shows that it consists of granular “mucus,” which, at an earlier stage, filled the cell-cavity, and which differs chemically from the cell-wall in that it is nitrogenous. This layer he proved to be never absent from living cells—to be, in fact, itself the living part of the cell, a discovery which was simultaneously (1846) made by Hugo von Mohl (1805–1872), who gave to the living matter of the plant-body the name “protoplasm.” In connexion with these discoveries, Naegeli controverted Schleiden’s view of the universality of free-cell-formation as the mode of cell-multiplication, and showed that in the vegetative organs, at least, new cells are formed by division. In the Zeitschrift, too, is Naegeli’s most important algological work—such as the paper on Caulerpa, which brought to light the remarkable unseptate structure of the Siphoneae, and his research on Delesseria, which resulted in the discovery of growth by a single apical cell. This discovery led Naegeli on to the study of the growing-point in other plants. He consequently gave the first accurate account of the apical cell, and of the mode of growth of the stem in various Mosses and Liverworts. Subsequently he observed that in Lycopodium and in Angiosperms the growing-point has no apical cell, but consists of a small-celled meristem, in which the first differentiation of the permanent tissues can be traced. One of the most remarkable discoveries recorded in the Zeitschrift is that of the antheridia and spermatozoids of Ferns and of Pilularia. The Beiträge zur wiss. Botanik consists almost entirely of researches into the anatomy of vascular plants, while the main feature of the Pflanzenphysiologische Untersuchungen is the exhaustive work on the structure, development and various forms of starch-grains. The Botanische Mitteilungen include a number of papers in all departments of botany, many of them being continuations and extensions of his earlier work. In his Theorie der Abstammungslehre Naegeli introduced the idea of a definite material basis for heredity; the substance he termed “idioplasm.” His theory of evolution is that the idioplasm of any one generation is not identical with that of either its progenitors or its progeny: it is always increasing in complexity, with the result that each successive generation marks an advance upon its predecessor. Hence variation takes place determinately, and in the higher direction only; while variability is the result of internal causes, and natural selection plays but a small part in evolution. Whereas, on the Darwinian theory, all organization is adaptive, according to Naegeli the development of higher organization is the outcome of the spontaneous evolution of the idioplasm.
More detailed accounts of Naegeli’s life and work are to be found in Nature, 16th October 1891, and in Proc. Roy. Soc., vol. li.  (S. H. V.*)