THE ORIGIN OF ORGANIC MATTER 17 



With the publication of "Recherches chimiques sur la vegetation" in 

 1804 by de Saussure a further step was marked in the development of the 

 subject. These investigations clearly indicate the tremendous change 

 which had been wrought by the new chemistry of Lavoisier. De Saussure 

 worked quantitatively, he asked certain questions and from his experiments 

 received definite answers ; he spoke a new language and followed a new 

 system of thought. He definitely established the necessity of carbon dioxide 

 for the development of plants and showed that a plant in a confined space 

 in which the respiration carbon dioxide was absorbed by potassium 

 hydroxide, soon succumbed. He also showed that plants in the light were 

 capable of using more carbon dioxide than is normally in the atmosphere 

 and that under such conditions showed increased growth — also that high 

 concentrations of carbon dioxide are deleterious to the plant. He further 

 demonstrated that oxygen is essential to the life of the plant ; in an at- 

 mosphere of nitrogen and carbon dioxide the plant cannot survive. The 

 quantitative relations between the amount of carbon dioxide fixed and 

 oxygen emitted were also studied by de Saussure : he thus introduced the 

 conception of the respiration and photosynthesis quotient. He also showed 

 the importance of water in the photosynthetic process, and was probably 

 the first to claim that carbon monoxide could not supplant carbon dioxide 

 in photosynthesis. His extensive investigations of the complex gaseous 

 exchange of succulent plants, such as cacti, were of fundamental signifi- 

 cance in elucidating the nature of the photosynthetic process under these 

 conditions and brought to light the intricate relations between organic acids 

 found in these plants and the apparently abnormal conditions of the photo- 

 synthetic quotient. Unfortunately de Saussure treated the earlier literature 

 of his subject very carelessly, so that from the reading of his works only, 

 one would be apt to gain a rather distorted conception of the historical 

 development of the subject. 



The quarter of a century ending with the publication of "Recherches 

 chimiques sur la vegetation" in 1804 in many ways witnesses greater in- 

 terest in the subject of photosynthesis than it has ever enjoyed. The 

 general interest in the subject waned decidedly. The botanists exhibited 

 very little regard : under the sway of the Linnean system, they occupied 

 themselves primarily with the describing and naming of new plants. While 

 Linne himself probably had higher aims, he had devised a method which 

 gave occupation to scores of botanists in the classification of plants, prob- 

 ably largely stimulated by the hope of the everlasting glory which falls to 

 the discoverer of a new si:)ecies. Although from a broad viewpoint photo- 

 synthesis is undoubtedly the most important function of the vegetable 

 kingdom, from the botanists it has never received the consideration its 

 importance demands. Hales, Priestley. Ingen-Housz. de Saussure were 

 not botanists in the sense of their day, they were chemists. They founded 

 the science of plant physiology, a division of the knowledge of plants 

 which until recently has been tolerated rather than encouraged by botanists. 



But it is not to any single cause or condition that the slow development 



