what he called " aerial acid," his name for carbon dioxide. Thus, 

 in a chemical laboratory, by a chemist, was made the discovery 

 of plant respiration. These experiments were afterwards con- 

 firmed by Lavoisier, the father of modern chemistry. 



In 1770, Jan Ingen-Housz, trying to straighten out the con- 

 tradiction of Priestley's experiments, placed green plants in sun- 

 light under water and showed that sunlight and leaf-green were 

 both necessary for the evolution of oxygen, but he thought that 

 the oxygen came from the water. Twelve years later Senebier 

 proved that the oxygen came from the plant, and resulted from 

 the carbon dioxide which the leaves had first taken from the 



Finally, in 1821 and 1822, Theodore de Saussure established 

 the fact that oxygen is indispensable to the life of the plant, and 

 that all parts of the plant, in darkness as well as in light, take in 

 oxygen and give off carbon dioxide. 



The famous Liebig, in 1841, rejected the entire theory that 

 plants respire, as based on " a weak and unstable foundation." 

 He considered that the carbon dioxide given off at night was 

 merely that taken in by the plant during the day, but not decom- 

 posed because of the absence of the sun's rays. To his great 

 prominence and authority may doubtless be attributed the per- 

 sistence, even to this day, of erroneous notions concerning plant 



It was Garreau who, in 185 1, insisted on the necessity of con- 



arate and distinct, and this position was afterwards accepted by 

 Sachs, and formulated into a general theory. 



I have given only the barest outlines of this history. The 

 battle raged long and fiercely over questions of fact and questions 

 of priority. But, fortunately for the world, the settlement of 

 scientific questions seldom, if ever, depends upon opinion or the 

 majority vote. They are not matters of opinion, and not debat- 

 able, but must be settled by direct appeal to nature, through 



C. Stuart Gager. 



