INTIlAMOLBCULAR EESPIKATION. 371 



of some other gas.^ The following experiment will illustrate 

 this : — 



If a mass of active seedlings be placed in a current of some 

 neutral gas, for instance nitrogen, tiie seedlings will continue to 

 evolve carbonic acid. Since the amount of carbonic acid given 

 off is greater than can be derived from the oxj'gen which might 

 bo fairly assumed to liave been retained in the plants at the be- 

 ginning of the experiment, the conclusion has been drawn that 

 tlie production of this gas is at the expense of substances within 

 the tissues containing combined oxygen. In other words, this 

 process, which is lilie respiration in some particulars, differs from 

 it in this respect : in ordinary respiration free oxygen enters into 

 the plant and there oxidizes certain matters ; while in this case 

 the molecules of certain compounds break up, and the released 

 oxygen at once forms, with carbon, carbonic acid, which is 

 evolved. This process is known as intramolecular respiration. 



982. Wortmann^ has proved that when seedlings of Vioia Faba 

 are placed for short periods in an atmosphere free from oxygen, 

 they give off the same amount of carbonic acid as they do when 

 oxygen is furnished. Hence he was naturally led to believe that 

 all the carbonic acid produced by plants has its origin in intra- 

 molecular respiration, and that the free oxygen of the air takes 

 no direct part in the formation of the carbonic acid evolved. 



983. But, on the other hand, Wilson' has shown that most 

 plants evolve much larger quantities of carbonic acid when free 

 oxygen is provided, and that Vicia Faba forms a remarkable 

 exception to this rule. His experiments were made upon seed- 

 lings, buds, leaves, flowers, fruits, and crj'ptogamous plants, 

 and with uniform results. He cites Pfeffer as saying: "If an 

 equal amount of carbonic acid were formed in both intramolecu- 

 lar and normal respiration, this would only prove that the same 



1 The same phenomenon has been observed in the case of some of the 

 lower animals : Pfliiger (Archives fur Pliysiologie, x., 1875, p. 251) has shown 

 that when these animals are kept in an atmosphere of nitrogen, they evolve 

 during the first few hours nearly the same amount of carbonic acid as if they 

 had been placed in common air. The chemical processes which cause the 

 production and evolution of carbonic acid in the absence of free oxygen are 

 grouped by Pfliiger under the term intramolecular respiration. 



2 Arbeiten des botanischen Instituts, Wiirzburg, 1880, p. 500. 



' Flora, 1882, and American Journal, xxiii., 1882, p. 423. For an interesting 

 account of the literature of intramolecular respiration see Pfliiger's paper, men- 

 tioned above. Observations upon the subject were made even during the last 

 century and early in the present century. For Broughton's and Pfeffer's work 

 see Botanische Zeitung, 1870, and Pflanzenphysiologie. 



