the Nitrogenous Matter of Plants. 119 



only principle we advance is that the living matter of plants and 

 animals has a similar chemical constitution, and that this mate- 

 rial in plants performs essential functions similar or analogous to 

 those of animals. 



It has for a long time been the general belief that plants, re- 

 versing the rule prevailing in animals, respire carbonic-acid gas, 

 which they extract from the soil or withdraw from the atmosphere, 

 and that whilst they assimilate its carbon they throw off its oxy- 

 gen — or that, in other words, a plant seems to respire by the 

 medium of an asphyxiating agent. However, when we consider 

 that the Fungi, the majority of Algae, the Orobanchese, the roots, 

 stems, flowers, the green fruits, &c. of all phanerogamic plants 

 constantly give off carbonic acid as a result of a process of com- 

 bustion between their carbon and the surrodnding oxygen, we 

 must feel obliged to admit that plants respire like animals, and 

 that the final result of the respiratory act consists, equally in the 

 two, in the decarbonization of their fluids or of their tissues, 

 and in the production of heat. 



M. Berard, in a prize thesis of the Academy of Sciences, has 

 shown that green fruits, even the youngest, exspire, whether in 

 sunshine or in the shade, notable quantities of carbonic acid. 1 

 have moreover proved, in a series of memoirs published in the 

 1 Annales des Sciences Naturelles/ by means of numerous experi- 

 ments, that buds and the young shoots succeeding them, adult 

 leaves, &c. consume a portion of their carbon by the aid of the sur- 

 rounding oxygen, or of that which they form within their tissues; 

 and that this function, which diminishes in activity as the leaves 

 grow old, is more marked when it proceeds under the influence 

 of a higher temperature. These facts, confirmed as they are by 

 the most recent researches, establish clearly enough that plants 

 are endowed with a respiratory function like that of animals, ex- 

 tending over the day as well as the night. At the same time it 

 must be granted that their diurnal animal respiration is rendered 

 more or less obscure in its results, as it can be accomplished by 

 the aid of the oxygen derived from the decomposition of the car- 

 bonic acid it produces, and which it incessantly gives off within 

 the laminae of their tissue or in the atmosphere. It is very easy 

 to demonstrate this double interchange by placing a green plant 

 or the leaves of one in a limited amount of atmospheric air, and 

 in the presence of some solution of baryta, when the latter will be 

 soon covered with a pellicle of the carbonate of that earth ; where- 

 as if the experiment be performed under the same conditions, 

 omitting the baryta, no trace of the carbonic-acid gas will be 

 discoverable. 



It is equally easy to establish the relation that subsists between 

 this act of animal respiration and the development of caloric from 



