In 1779, the Dutch physician Jan Ingen-Housz (1730–1799) obtained a leave-of-absence from his post as Court Physician to Empress Maria Theresa of Austria in order to do research (in England) on plants during the summer months. He performed more than 500 experiments, and described the results in his exceptional book Experiments Upon Vegetables (1779). In addition to proving the requirement for light in photosynthesis, Ingen-Housz established that leaves were the primary sites of the photosynthetic process. Later, Ingen- Housz published research papers on various subjects but aside from his 1779 book, he published only one more communication on photosynthesis and plant physiology. This was entitled 'An Essay on the Food of Plants and the Renovation of Soils'. The essay was published in 1796 as an appendix to an obscure British government report, which is rare and virtually unknown. The present paper describes the 1796 essay, which is particularly interesting in that it shows how Ingen-Housz's concepts were modified by new interpretations of chemical phenomena described in Lavoisier's great and revolutionary book Traité Élémentaire de Chimie (1789). Ingen-Housz not only discovered photosynthesis, but plant respiration as well, and the 1796 essay is testimony to his remarkable insights.