7 o THE POPULAR SCIENCE MONTHLY. 



the air in the tube. The acid was absorbed, as soon as formed, by the 

 alkaline solution, and the latter rose in the tube until there was no gas 

 left except nitrogen. 



The bud was kept in the nitrogen till May 2d ; it then began to give 

 signs of decay. During all this time it never gained in size, and re- 

 tained its original form. The conclusion is, that bud development can- 

 not go on in an atmosphere deprived of oxygen. 



We know, further, from the observations of Th. de Saussure, that 

 germination is impossible when the embryo, in process of growth, does 

 not find, in the atmosphere in which it lives, the amount of oxygen 

 needed for its life. Hence Corenwinder's experiment gives us a fresh 

 instance of the resemblance between germination and the evolution of 

 leaf-axes. 



Th. de Saussure also examined several plants placed in an atmos- 

 phere of nitrogen. According to their behavior under these circum- 

 stances, he divides them into two categories, viz., those which vegetate 

 in such an atmosphere only for a few days, and those which live and 

 even flourish there for a certain length of time. Plants of the latter 

 class are chiefly those which inhabit marshy situations, such as JLyth- 

 rum salicaria, Epilobium hirsutum, Polygonum amphibium, etc. He 

 has expressed the opinion that plants possessed of this latter property 

 consume less oxygen, vegetating in atmospheric air without much light. 



If, in M. Corenwinder's experiments, plants wither rapidly, the rea- 

 son is, that in the morning he drew off the carbonic acid formed dur- 

 ing the night by the agency of the oxygen contained in the cells. 

 When this is not done, the leaves may decomjjose the acid in the day- 

 time, give out oxygen, and so live for a long time, the oxygen being 

 inhaled and exhaled over and over again. 



Finally, if the leaves be kept in absolute darkness, the reducing 

 action is null, and then the act of respiration, which, of necessity, is 

 never completely suspended, alone appears, and the plant disengages 

 only carbonic acid. This function, however, is curiously affected by 

 temperature, so that, at 32 Fahr., leaves usually exhale but little car- 

 bonic acid. 



These early observations would of themselves suffice to show the 

 existence in plants, at every stage of growth, of a respiratory action, 

 like that of animals, viz., an absorption of oxygen. 



What in the books is called the diurnal respiration of plants, is in 

 reality an assimilation of carbon ; in other words, it is the act whereby 

 the leaf-organs decompose the carbonic acid of the air, and give out its 

 oxygen. This act depends essentially on the influence of light. It is 

 at the maximum intensity when the plant is under the direct action of 

 the sun's rays, and gradually diminishes in importance in proportion 

 as the light grows feebler ; for instance, when the sky is overcast with 

 clouds, and when the weather is thick and rainy. This was demon- 

 strated in a memoir by Corenwinder, published in 1858. 



