Life and Writings of Theodore de Saussure, 15 



tion, and proportionate to the size of the seed, are very minute, 

 and do not carry off, in the case of wheat and barley, for ex- 

 ample, more than a thousandth part of their weight. The 

 seed loses, at the same time, a small portion of its fixed and 

 elementary water. This result, however, takes place, not in 

 the very act of germination, but after the seed is dead, and 

 while it is drying. Light appears to have no influence on the 

 germination of seeds, contrary to the opinion of Senebier, who 

 believed that it was hurtful to the process. 



The author then considers the influence of carbonic acid on 

 vegetation. This gas, in which seeds cannot spring, and which 

 has no well-marked influence in stimulating the vegetation of 

 plants recently germinated, is the principal agent of vegetation 

 in plants which have reached their complete state of develop- 

 ment. In the sun, every augmentation in the quantity of car- 

 bonic acid in the water which contained the roots of the plants, 

 or in that of the air which surrounded them, accelerated nu- 

 trition and increased the vigour of the plants. When, on 

 the contrary, all the carbonic acid of the air or water was re- 

 moved by means of quick-lime, plants standing in the sun soon 

 died, and vitiated their atmosphere. The same results did not 

 appear in the night, the carbonic acid, on the contrary, then 

 seeming to be hurtful to the health of plants. By causing 

 plants to vegetate in artificial atmospheres with all the ele- 

 ments of which he was acquainted, Theodore de Saussure satis- 

 fied himself not only that the green part of plants decom- 

 posed carbonic acid under the influence of the solar rays, as 

 Senebier had previously announced, but that they appropriated 

 all the carbon, and a small part of the oxygen gas, of this car- 

 bonic acid, restoring the rest or the great part of the oxygen 

 gas, to the air. He then shewed that the same fixation of 

 carbon took place in the open air, in plants which could not 

 derive it from the soil which carried them, and which, in con- 

 sequence, could not draw it but from the carbonic acid of the 

 atmosphere. These experiments of Theodore de Saussure, by 

 proving, that if the proportion of the carbonic acid of the air 

 was augmented, vegetation would derive from it greater ac- 

 tivity, have thrown great light on the possibility of the forma- 



