CHLOROPHYLL AND ENERGY 153 



night, plants did not purify the air but vitiated it, as did the 

 breath of animals. 



Senebier, a Swiss, resumed the experiment that Bonnet had 

 so misinterpreted and showed that, if green leaves plunged in 

 water released bubbles, they could do so only in the presence 

 of carbon dioxide that sunlight enabled them to decompose. 



At the beginning of the nineteenth century, the great Swiss 

 physiologist, Theodore de Saussure, assembled all these ideas, 

 extracted what was valuable from them and demonstrated the 

 action of the plants by well-arranged experiments. Thanks to 

 him, the problem was clearly posed, and he estabUshed a 

 schedule exact enough to show that the increase in substance 

 exceeded the weight of carbon retained : carbon combined with 

 the elements of water in the plant to form plant material. 



It was difficult at that time to say more, and A. de CandoUe 

 wrote, in 1835, with a charming naivete, that there did not 

 seem to be many more discoveries to be made in this field. 



"As a result of the work, in particular, of Senebier and of 

 Theodore de Saussure, the circumstances and consequences of 

 plant respiration are today very well known. 



"The only organs showing this phenomenon are the parts 

 coloured green, principally the leaves. The green colour is not 

 the cause of the chemical action; it is, on the contrary, the 

 effect of it. It would be more exact to say that plants and 

 organs which give off oxygen are coloured green or that they 

 become so ; but as it is easier to judge of the colour than of the 

 chemical action, we use rather the reverse expression and say 

 that oxygen is given off by the green parts. The colour is an 

 indication and a criterion."^ 



It was not until the German, Sachs, linked assimilation 

 with chlorophyll and the chloroplasts that justice was done 

 to the green parts. "Carbon is fixed by the leaves in the form 

 of starch from which all the organic products are elaborated." 



Thus was defined the role of photosynthesis that the 

 French physiologists, Garreau, Boussingault and Claude 

 Bernard, had just clearly distinguished from respiration. 



^Introduction a V etude de la botanique, I, page 264. 



