De Saussure, Nicolas-Théodore

Swiss botanist 1767–1845

Nicolas de Saussure was an early pioneer in plant physiology. He was born and lived in Geneva, Switzerland, and later became professor of mineralogy and geology at the Geneva Academy. De Saussure's most famous book was Recherches chimiques sur la végétation, or "Chemical Research on Plant Matter," published in 1804.

De Saussure studied gas and nutrient uptake in plants, using the scientific method of controlled experimentation. By enclosing plants in glass containers and weighing the plants and enclosed carbon dioxide before and after, de Saussure demonstrated that plants absorb carbon dioxide during photosynthesis. This showed that carbon in plants comes from the atmosphere (not the soil, as some believed). Extending the work of Jan Ingenhousz, who showed oxygen was released during photosynthesis, de Saussure proved that the volume of carbon dioxide absorbed is approximately equal to the volume of oxygen consumed. Because the weight of carbon absorbed was less than the total weight increase of the plant, de Saussure reasoned that water is absorbed, and in so doing correctly outlined the major chemical transformations in photosynthesis.

De Saussure also studied oxygen consumption in germinating seeds and plants grown in the dark, and argued (correctly) that the use of oxygen by plants was similar to that of animals. Later in life, he analyzed plant ashes to show that the mineral composition differed from that of the soil, thereby demonstrating that plants absorb nutrients selectively.

SEE ALSO VAN Helmont, Jan ; History of Plant Physiology ; Ingenhousz, Jan ; Photosynthesis

Richard Robinson

Bibliography

Morton, Alan G. History of Botanical Science. New York: Academic Press, 1981.