82 STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 



activity the leaves have a relatively low supply of oxidizable material, 

 resulting in correspondingly low respiration rates. Therefore, the 

 experimental conditions in the investigations of Willstaetter and 

 StoU were destined to give more definite results. 



In just what manner respiration can participate in the photo- 

 synthetic process it is as yet impossible to say with any degree of 

 certainty. That the heat liberated in the process of plant respiration 

 is to be regarded largely as an energetic waste product now seems 

 highly probable. 



If respiration is to be considered as a producer of energy for the 

 maintainance of the so-called life processes, the potential energy of 

 the food materials can not be converted entirely into heat, for if 

 that were the case the heat of respiration could be substituted by heat 

 applied from without. This, of course, is not the case. There must 

 be produced in the course of respiration other forms of energy which 

 are used in the metabolic processes of the plant. That such is the 

 case was indicated in the old experiments of Bonnier,^ who found 

 that considerably less heat was evolved than could be expected from 

 the respiratory coefficient. Further calorimetric studies of this 

 kind would be highly desirable, carried out on the basis of knowledge 

 obtainable regarding the transformation of the carbohydrates and 

 other food material and with the application of modern temperature- 

 measuring devices of high accuracy. While such calorimetric 

 investigations would serve as excellent guides and checks, it is 

 evident that they can tell us little of the more intricate details of 

 the energy release in respiration. 



Besides heat, then, it would appear that the plant has available 

 and uses a considerable amount of energy derived from the breaking 

 down and combustion of carbohydrates and other food material. 

 Plant physiologists have widely accepted the dictum that this energy 

 is converted into work by the plant. The nature of the work which 

 is thus performed by the combustion of organic substances has been 

 described in only vague and indefinite terms, although it is the basic 

 problem of plant life. In the case of animals, where the factors of 

 locomotion, balance, and other purely mechanical movements are 

 involved, the work done is of a far more evident nature.^ In the 

 plant, however, it requires rather more searching perception to 

 determine in what manner this release of energy in respiration takes 

 form, for it is a strictly chemical phenomenon. The discussion here 

 is limited to the energy liberated by the breakdown and oxidation 

 of food material. The tensions and pressures related to turgor or 

 the possible mechanical work involved in the activity of the so-called 



1 BoNNiEE, G. Ann. Sci. Nat. Bot., (7), 18, 1 (1893). 



Spoehr. H. A. Carnegie Inst. Wash. Pub. No. 287, 21 (1919). 

 « Oppenheimek, C. Der Mensch als Kraftmachine. Die Naturwiesenschaften, 23, 64-72 (1920). 



