12 HISTOKICAL INTRODUCTION. 



next step in this highly interesting and important 

 discovery was taken by John Ingenhousz (1730-1799), 

 an eminent physician and natural philosopher. In 

 1779, Ingenhousz published a work in London entitled 

 * Experiments on Vegetables.' In it he gives the 

 results of some important experiments he had made 

 on the question already investigated by Bonnet and 

 Priestley. These experiments proved that plant- 

 leaves only gave up their oxygen in the presence of 

 sunlight. In 1782 he published another work on 

 'The Influence of the Vegetable Kingdom on the 

 Animal Creation/ l 



The source of the gas, which Bonnet had first 

 noticed to be given off from plant-leaves, Priestley had 

 identified as oxygen, and Ingenhousz had proved to be 

 only given off under the influence of the sun's rays, 

 was finally shown by a Swiss naturalist, Jean Senebier 2 

 (1742-1809), to be the carbonic acid gas in the air, 

 which the plant absorbed and decomposed, giving out 

 the oxygen and assimilating the carbon. 



deleterious action on plant -growth. Percival was really the first to 

 point out that carbonic acid gas was a plant-food. 



1 It is recorded as an instance of the scientific enthusiasm of the 

 man, that he was wont to carry about with him bottles containing 

 oxygen, which he had obtained from cabbage-leaves, as also coils of 

 iron wire, with which he could illustrate the brilliant combustion 

 which ensued on burning the latter in oxygen gas. 



2 For a full account of Senebier's researches, see l Physiologic 

 vegetale, contenant une description des organes des plantes, et une 

 exposition des pheuomenes produits par leur organisation, par Jean 

 Senebier.' (5 tomes. Geneve, 1800.) 



