FORMS OF ENERGY IN THE PLANT 



401 



and friction, e. g. the friction of water against the walls of the vessels. What 

 part these processes severally play in heat production we do not know, but we 

 cannot be far wrong in assuming that they are only of secondary importance, 

 and that respiration is actually the chief factor in the evolution of heat energy 

 by the plant. 



If, however, the total amount of energy in the materials oxidized in respira- 

 tion, i. e. chemical energy, is released in the form of heat, we must revise our 

 previous conception of the significance of respiration. Should respiration be 

 the source of the energy required to maintain vitality, chemical energy cannot 

 be entirely transformed into heat, otherwise it would be possible to replace the 

 energy released in respiration by heat energy obtained from external sources, 

 which, as already seen, is not the case. Other forms of energy must obviously 

 be produced by respiration, which cannot originate in any other way. Heat is 

 only a by-product, it might almost be termed a loss of available energy. This 

 holds at least for the majority of plant organs but cannot be true of all ; mani- 

 festly, it is not in agreement with the great evolution of heat from many flowers. 

 In Arum italicum, for example, the spadix is the special organ in which heat 

 is produced. This spadix, before the flowering-period, consists, according to the 

 researches of G. Kraus (1894-5), of about three-fifths water and two-fifths 

 dry substance, 80 per cent, of which latter consists of carbohydrate. The 

 carbohydrate is, in the course of a few hours, completely used up and evidently 

 decomposed into water and carbon dioxide, while the nitrogenous constituents 

 remain intact. The spadix is, however, a mature organ whose function disap- 

 pears soon after the flowering-period is over, and which exhibits certain special 

 activities during this rapid combustion, which we cannot conceive of as 

 occurring in growing organs. In this case the conclusion cannot be avoided 

 that the carbohydrate is exclusively employed for the production of heat. 

 But that all such collections of material are employed for the production of heat, 

 to the exclusion of all other uses, is a proposition not to be entertained. Hence 

 one is compelled to believe that the heat evolved in Arum italicum and in 

 such flowers as produce large amounts of heat is not a useless by-product but 

 a special adaptation for attracting insects, as Delpino (1870), and Kraus 

 (1894-5) have suggested. We may at least consider heat production in flowers 

 as a phenomenon sui generis, having nothing to do biologically with heat 

 production in other organs, although, looked at from a purely physiological 

 standpoint, the heat is produced in the same way as it is in ordinary respiration 

 in all plants and all organisms. 



Although at present we are, generally speaking, unable to present a com- 

 plete and comprehensive explanation of the phenomenon of heat production 

 in plants, still, the way to reach such an explanation is clearly indicated. For 

 that purpose it is necessary to make comprehensive calorimetric investiga- 

 tions which alone would afford a basis for conclusions as to the amount of heat 

 as compared with the total of energy released in the process of respiration. 



Imperfect as our knowledge is of the phenomena connected with the 

 evolution of heat, it is extensive as compared with what we know as to the 

 production of light by plants. It is true that luminosity is of much rarer 

 occurrence and hence of less general interest, limited as it is to certain groups of 

 Fungi and Bacteria [Molisch, 1904]. (For literature see Verworn, 1901). 

 The phenomenon is closely connected with vital processes, although we have net 

 as yet been able to isolate from the organism any substance which emits light 

 rays, although, certain non-living compounds are known to be luminous. 

 Luminosity cannot be accounted for by a previous storage of light, for it is 

 quite independent of precedent illumination ; luminous Bacteria and rhizo- 

 morphs emit light rays in continuous darkness. There can be no doubt that 

 luminosity bears the same relation to respiration as heat does, for it is manifested 

 only when oxygen is supplied in abundance. We further know that luminosity 

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