5oo Theory of the Nutrition [BOOK in. 



printing a definite quantity of carbon make a much more than 

 proportionate addition to their dry substance, and that this is 

 due to the simultaneous fixation of the component parts of 

 water. The full significance of this fact could only be appre- 

 hended at a later time, when the theory of the combinations of 

 carbon, organic chemistry, had been further developed. As 

 regards the importance of the decomposition of carbon dioxide 

 by the green organs under the influence of light to the whole 

 nourishment of the plant, de Saussure arrived by more definite 

 proofs than Ingen-Houss had given at the result, that only 

 a small portion of the substance of plants is derived from the 

 constituents of the soil in solution in water, but that the great 

 mass of the vegetable body is built up from the carbon dioxide 

 of the atmosphere and the constituents of water ; he con- 

 vinced himself of this partly by considering the small quantities 

 of matter which the water is able to dissolve from a soil capable 

 of sustaining vegetation, partly by experiments in vegetation 

 and considerations of a more general character. 



Not less important were de Saussure's investigations into 

 oxygen-respiration by plants, which taken simply as a fact, had 

 been previously discovered by Ingen-Houss. But de Saussure 

 showed that growth is impossible without this process of re- 

 spiration, even in germinating plants, though these are rich in 

 assimilated matter. He further showed that green leaves and 

 opening flowers, and generally the parts of plants which are 

 distinguished by greater activity of vital processes, require more 

 oxygen for respiration than those in a less active and resting 

 state. He determined the loss of weight which the organic 

 substance of germinating plants suffers from respiration, and 

 found it to be greater than was proportionate to the weight of 

 carbon exhaled ; but the chemical science of his day did not 

 supply him with a certain explanation of this fact. Lastly, 

 de Saussure at a later time (1822) discovered the chief relations 

 between the internal heat of flowers and their consumption of 

 oxygen, and thus we see that he supplied the most important 



