Carl Nägeli

Carl Nägeli (1817–1891) was a Swiss botanist whose studies of plant cells and heredity shaped nineteenth-century biology. He proposed idioplasm as a hereditary substance and corresponded with Charles Darwin.

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Charles Darwin: Charles Darwin was an English naturalist who developed the theory of evolution by natural selection. Darwin corresponded with Nägeli and sought his explanation for why natural selection did not produce certain changes.
Cell theory: Cell theory holds that organisms are composed of cells and that cells arise from preexisting cells. Nägeli’s studies of plant development and cell division addressed a central subject of cell theory.
Idioplasm: Idioplasm was Nägeli’s hypothetical hereditary substance, thought to organize development and transmit traits. This was Nägeli’s central proposal for explaining heredity and the direction of variation.
Mendelian inheritance: Mendelian inheritance describes the transmission of traits through discrete hereditary units that segregate and recombine. Nägeli’s failure to recognize Mendel’s findings became a notable episode in the delayed reception of Mendelian genetics.
Gregor Mendel: Gregor Mendel was an Austrian monk whose pea-plant experiments established principles of inheritance. Nägeli corresponded with Mendel about heredity, though he did not recognize the significance of Mendel’s results.
Mitosis: Mitosis is the process by which a eukaryotic cell divides its nucleus into two genetically similar nuclei. Nägeli studied cell division in plants, helping document how new cells arise.
Germ plasm: Germ plasm is the hereditary material in reproductive cells, distinct from the body’s other tissues. August Weismann’s later theory offered a different account of hereditary continuity than Nägeli’s idioplasm.
Neo-Lamarckism: Neo-Lamarckism is a family of evolutionary theories that assign evolutionary importance to acquired traits or direct environmental effects. Nägeli’s emphasis on internal hereditary forces differed from explanations centered on environmental effects.
Matthias Jakob Schleiden: Matthias Jakob Schleiden was a German botanist who helped establish the cell theory of plants. Nägeli’s botanical research developed within the cell-theory tradition Schleiden helped establish.
Plant anatomy: Plant anatomy is the study of the internal structures of plants, including their cells and tissues. Nägeli’s botanical work examined plant structures at cellular and tissue scales.