THE RESPIRATION OF PLANTS. 61 



the immediate principles of food, and animal life destroyed them; the 

 various excretions of animal life were the natural ferment of vegetal 

 life, and the latter purified the air, contaminated by animal emanations ; 

 finally, that function of the organism which is most continuous, name- 

 ly, respiration, consisted, in animals, in the absorption of oxygen, fol- 

 lowed by exhalation of carbonic acid, while in plants it consisted in 

 the absorption of carbonic acid, followed by exhalation of oxygen. 

 In this way the respiration of plants would decompose the carbonic 

 acid produced by the respiration of animals, thus preserving the nor- 

 mal constitution of the atmosphere. 



The famous experiments of Claude Bernard on the glycogenic 

 function of the liver, revealing, as they did, the formation in the 

 liver of animals of one of the most important of these immediate 

 principles, to wit, sugar, delivei-ed on this apparently philosophic and 

 well-established theory a severe blow, from which it could not recover. 

 Soon, a very different theory, one no less philosophic in its general 

 form, was proposed ; and this theory was so bound up with the ten- 

 dencies of modern science and philosophy, that its success was assured 

 from the outset. In place of the harmonic contrast of the two king- 

 doms, we have now the functional unity of living Nature. Our read- 

 ers have not forgotten the lectures delivered dm*ing several years by 

 Claude Bernard, at the Paris Museum of Natural History, in which he 

 has developed this grand conception. Instead of comparing together 

 animals and plants, pointing out their differences, as the usual course 

 has been, Bernard enumerates their resemblances ; and this simple 

 change in the point of view at once gives to the ensemble of the facts 

 a very different meaning. 



But, still there appear to remain some fundamental differences, 

 chiefly with regard to respiration. 



Since the date of the early researches, which made out the respira- 

 tion of plants to be an exhalation of oxygen resulting from the decom- 

 position of the carbonic acid of the atmosphere, sundry not very recent 

 experiments have to a certain extent limited the bearings of the origi- 

 nal conclusions. It was soon discovered that this mode of respiration 

 is subordinated to the action of solar light, and that it occurs only in 

 the leaves and in the green portions of the plant, the coloration being 

 due to the presence of a special principle called chlorophyll; and thus 

 the chlorophyll came to be regarded as the organ, the essential agent 

 of plant-respiration. Next, the discovery was made that the flowers 

 of a color different from green, and even the green portions themselves 

 when placed in the dark, not only do not absorb carbonic acid out of 

 the atmosphere, and then exhale the oxygen of that acid ; they go 

 further, and do the very opposite, absorbing oxygen and giving up 

 carbonic acid, just as animals do. 



Hence the assignment to plants of a second mode of respiration, 

 known as nocturnal, as opposed to the other mode, called the diurnal 



