On March 9, 1845, German botanist and plant physiologist Wilhelm Pfeffer was born. Pfeffer’s work on osmotic pressure made him a pioneer in the study of plant physiology. With Julius von Sachs, he was a leader in systematizing the fundamentals of plant physiology.
Wilhelm Pfeffer attended the University of Göttingen studying chemistry and pharmacy under the chemist Friedrich Wöhler who became best known for his synthesis of urea, under William Eduard Weber who became known together with Carl Friedrich Gauss as the inventor of the first electromagnetic telegraph, and Wilhelm Rudolph Fittig who for instance discovered the pinacol coupling reaction, mesitylene, diacetyl and biphenyl. Pfeffer later switched to the University of Marburg and the University of Berlin. At the latter, Wilhelm Pfeffer was able to study under the botanist Alexander Braun. Pfeffer further became assistant to the botanist Nathanael Pringsheim and served as an assistant to Julius von Sachs in Würzburg.
Pfeffer was first appointed professor of pharmacology and botany at the University of Bonn in 1873. He later became professor at the University of Basel and the University of Tübingen. At the latter, Wilhelm Pfeffer also served as director of the botanical garden. During the 1880s, Pfeffer was appointed professor at the University of Leipzig and director of its botanical garden. During his time at Leipzig, Pfeffer published a work on the use of photography to study plant growth. He intended to extent the chronophotographic experiments of the French scientist, physiologist and chronophotographer Étienne-Jules Marey through producing a short film involving the stages of plant growth.
As one of the pioneers of modern plant physiology, Wilhelm Pfeffer researched the thermonastic and photonastic movements of flowers, the nyctinastic movements of leaves, protoplastic physics and photosynthesis. During his time at Basel, Pfeffer researched plant metabolism and developed a a semi-porous membrane to study the phenomena of osmosis. The developed osmometric device became known as the ‘Pfeffer cell’ and was used for determining the osmotic pressure of a solution. Osmotic pressure is the minimum pressure which needs to be applied to a solution to prevent the inward flow of its pure solvent across a semipermeable membrane. It is also defined as the measure of the tendency of a solution to take in pure solvent (which belongs to the solution under discussion) by osmosis. The phenomenon of osmosis arises from the propensity of a pure solvent to move through a semipermeable membrane and into its solution containing a solute to which the membrane is impermeable. This process is of vital importance in biology as the cell’s membrane is semipermeable.
Wilhelm Pfeffer was elected a member of the Royal Swedish Academy of Sciences in 1897. His library of more than 11.000 works now belongs to the Okayama University in Japan.
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