Schleiden and Schwann's cell theory

Plant cells had been familiar to microscopists for a long time, and in 1831 the botanist Robert Brown described the nucleus in orchid cells. Animal tissues seemed too varied to share a single plan, and plants and animals were thought to grow in different ways. Matthias Schleiden, studying how new plant cells form, concluded that cells were the structural units of all plants and published his account in Johannes Müller's Archiv in 1838.

Schleiden told Theodor Schwann, Müller's favorite pupil, about his results in October 1837, before they were printed. In Schleiden's scheme a new cell started as a small vesicle rising on the nucleus, which he called the cytoblast. Schwann had already noticed that the notochord and the gill cartilage of tadpoles looked like plant tissue, and Schleiden's findings led him into wider studies of animal tissues.

His book of 1839 argued that one common principle of development underlay the elementary parts of all organisms, plant and animal. He treated blood corpuscles and the cells of epithelium, cartilage and plants as versions of the same unit, and he showed that very different tissues grow from cells that at first look alike. He compared the process to crystals, which take many shapes but form by the same laws.

Both men were wrong about how new cells arise; Hektoen International's account says they believed new cells formed from crystallized remnants of old nuclei. Robert Remak confirmed cell division in animal cells as early as 1844, and Rudolf Virchow published Remak's findings in 1855. Schwann also coined the word metabolism, and the Schwann cell of nerve fibers, described in the same 1839 book, carries his name.