Jean Sénébier (1742-1809). Jean Senebier was a Swiss pastor and botanist from Geneva. He established that carbon dioxide (fixed air) was essential to photosynthesis. He showed that plants absorb carbon dioxide and release oxygen (dephlogisticated air) (Govindjee and Krogmann 2005).
His research on plants was encouraged by the discovery of Jan Ingenhousz in1780 that a green leaf did not produce “dephlogisticated air” in boiled distilled water.This means that where water does not contain carbon dioxide, a submerged leaf does not produce oxygen. However, it was Jean Senebier who later made the conclusion (Egerton 2008).
For his experiments, he used “only healthy plants grown under standard conditions.” He found that illuminated leaves that were submerged in water without dissolved carbon dioxide did not release oxygen, but more oxygen is liberated in water saturated with carbon dioxide than in ordinary water. Further, mere illumination did not produce oxygen even from water saturated with CO2. He confirmed his findings in similar experiments using “shoots in air” but still maintained (erroneously) that “plants obtain CO2 only from that dissolved in water, humid air and droplets of dew on leaves” (Journal of Experimental Botany 1985).
It was in 1782 that Jean Senebier published his Mémoires physico-chimiques sur l’influence de la lumière solaire pour modifier les étres des trios règnes de la nature et surtout ceux du règne vegetal. He noted that “fixed air” must be present for plants to make “dephlogisticated air”. Believing that “fixed air” was a mixture of “phlogisticated air” (N2) and “pure air” (O2), he formulated a concept of plant-air interaction consisting of the following cycle (Egerton 2008):
(1) a plant absorbs “fixed air” (“dephlogisticated air” mixed with phlogiston) from the ground through its roots --->(2) the plant releases “dephlogisticated air” to the atmosphere through its leaves --->(3) dephlogisticated air mixes with phlogiston which is present in the atmosphere to form “fixed air” --->(4) fixed air is precipitated toward the earth surface --->(5) fixed air is dissolved in rain and ground water --->(6) back to 1.
He later abandoned his belief in phlogiston. In his Expériences sur l’action de la lumière solaire dans la vegetation, published in1788, Jean Senebier apparently adopted Lavoisier’s chemistry and used some of the new terms that the latter introduced such as hydrogen and oxygen. Ingenhousz did the same a year later. Translated by Nash (1957, cited by Egerton ), Senebier said:
“Since plants contain hydrogen whether they grow in sand, in sponge, or in powdered glass, it is evident that the plants do not obtain the hydrogen from these substances…light and water is indispensable to vegetation. Light does not contain inflammable air, while water does. Therefore it appears that one may believe that if some parts of plants relieve the water of its hydrogen, by combining with the latter, the oxygen must escape from the plant by the action of sunlight….”
In 1796 Jan Ingenhousz finally agreed with Jan Senebier that carbon dioxide is taken up and decomposed in green leaves and oxygen is released into the air (Egerton 2008).
(Ben G. Bareja. June 2012)
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