Wilhelm Pfeffer

German botanist and plant physiologist

Wilhelm Friedrich Philipp Pfeffer (9 March 1845 – 31 January 1920) was a German botanist and plant physiologist born in Grebenstein.

He studied chemistry and pharmacy at the University of Göttingen, where his instructors included Friedrich Wöhler (1800 1882), William Eduard Weber (1804 1891) and Wilhelm Rudolph Fittig (1835 1910). Afterwards, he furthered his education at the universities of Marburg and Berlin. At Berlin, he studied under Alexander Braun (1805 1877) and was an assistant to Nathanael Pringsheim (1823 1894). Later on, he served as an assistant to Julius von Sachs (1832 1897) at Würzburg,

In 1873 he was appointed professor of pharmacology and botany at the University of Bonn, followed by professorships at the Universities of Basel (from 1877) and Tübingen (from 1878), where he also served as director of the Botanischer Garten der Universität Tübingen. In 1887 he became a professor at the University of Leipzig and director of its botanical garden. He was elected a member of the Royal Swedish Academy of Sciences and an International Honorary Member of the American Academy of Arts and Sciences in 1897, an International Member of the United States National Academy of Sciences in 1903, and the American Philosophical Society in 1909.

Pfeffer was a pioneer of modern plant physiology. His scientific interests included the thermonastic and photonastic movements of flowers, the nyctinastic movements of leaves, protoplastic physics and photosynthesis. In 1877, while researching plant metabolism, Pfeffer developed a semi porous membrane to study the phenomena of osmosis. The eponymous "Pfeffer cell" is named for the osmometric device he constructed for determining the osmotic pressure of a solution. During his tenure at Leipzig, Pfeffer published an article on the use of photography to study plant growth. He wanted to extend the chronophotographic experiments of Étienne Jules Marey (1830 1904) by producing a short film involving the stages of plant growth. This "movie" would be filmed over a period of weeks by frame at a time exposure taken at regular spaced intervals. Later, time lapse photography would become a commonplace procedure.