(1804–81), German botanist, who, with the German physiologist
Theodor Schwann, formulated the cell theory (see 
CELL,).
Born in Hamburg and educated in law at Heidelberg, Schleiden left
law practice to study botany, which he then taught at the University
of Jena from 1839 to 1862. A man of disputatious nature, he scorned
the botanists of his day who limited themselves to merely naming
and describing plants. Schleiden investigated plants microscopically and
conceived that plants were made up of recognizable units, or cells.
Plant growth, he stated in 1837, came about through the production
of new cells, which, he speculated, were propagated from the nuclei
of old cells. Although later discoveries proved him wrong about
the role of the nucleus in mitosis, or cell division, his conception
of the cell as the common structural unit of plants had the profound
effect of shifting scientific attention to living processes as they
happened on the cellular level—a change that initiated
the field of EMBRYOLOGY, (q.v.).
A year after Schleiden published his cell theory on plants, his
friend Schwann extended it to animals, thereby bringing botany and
zoology together under one unifying theory.
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