Nicolas-Théodore de Saussure (French pronunciation: [nikɔla teɔdɔʁ də sosyʁ]; 14 October 1767 – 18 April 1845[1]) was a Swiss chemist and student of plant physiology who made seminal advances in phytochemistry.

[2] Nicolas-Théodore de Saussure was born into a wealthy, aristocratic, Genevan family, many of whose members were accomplished in the natural sciences, including botany.

(While his father was alive, Théodore's papers were published under the name "de Saussure fils", as was the custom of the day for the sons of scientists having the same surname.

[10] He lived quietly and somewhat reclusively, doing research in his own private laboratory (as was the custom for scientists of his day), but, like others in his family, he was active in public affairs in Geneva,[9] and he served on the Genevan representative council.

[13] As a young man, Nicolas-Théodore accompanied his father on his Alpine expeditions, some of them under arduous conditions, and assisted him with experiments in physics, chemistry, mineralogy, and meteorology.

[19] His early papers on these subjects laid the groundwork for some of the chapters in his magnum opus, Recherches chimiques sur la Végétation ("Chemical Research on Plant Growth"), published in 1804.

He demonstrated this by showing that plants grown with their roots in water and their shoots in an atmosphere of ordinary air with added CO2 increased in dry weight by an amount much greater than could be attributed to the assimilation of the CO2 gas available to them.

[23] In addition, field research by French agricultural chemist Jean-Baptiste Boussingault substantiated Saussure's conclusions on the importance of mineral nutrients that plants take up from the soil.