DEPARTMENT OF BOTANICAL RESEARCH. 79 



atmospheres enriched with carbon dioxid. So far as has been investi- 

 gated, this interdependence of respiration and photosynthesis appHes 

 not only in the course of activity of individual leaves, but also to the 

 differences exhibited between different species. 



From all of our experiments thus far completed, a metabolic inter- 

 pretation of the phenomenon of photosynthesis seems most plausible. 

 That is in the sense that the energy released in the processes of respira- 

 tion contributes to the series of endothermal reactions involved in the 

 synthesis of carbohydrates. The radiant energy absorbed thus would 

 be considered as complemental in the reaction, and the whole process 

 might be placed under that group of chemical changes designated as 

 coupled reactions. 



The most profitable conception of photo-chemical change is that 

 which is based upon the principle of photo-electricity, and this favors 

 the Luther theory that prerequisite to a photo-chemical reaction is the 

 loosening of electrons. In applying the results and conceptions of 

 photo-electricity to the process of photosynthesis it must be borne in 

 mind that pure photo-chemical reactions have very small temperature 

 coefficients. However, it has been known for a long time that the 

 photosynthetic activity of a plant is very decidedly affected by tem- 

 perature. 



The manner in which the energy released by the respiratory actions 

 is utilized by the plant is still entirely unknown. Probably the most 

 noteworthy result of the energy release of respiration in plants is the 

 formation of new compounds. These compounds may be designated 

 as of higher energy content, although they may not again serve the 

 plant as food material, but enter only into structural or plasmic ele- 

 ments of the organism. The yield of new material thus formed is 

 indeed usually very low as compared with the total amount of material 

 consumed in the respiratory activity. The important point, however, 

 for the present consideration, is the fact that the breaking-do\\'n of 

 food material, such as the relatively simple monosaccharids, yields 

 energy in such a form and manner as to make possible these synthetic 

 activities. Since the photosjTithetic activity is greatly increased by 

 the same agencies and conditions which augment respiratory activity, 

 i. e., by those factors which afford a greater release of energy, it would 

 appear that such a greater release of energy favors a higher synthetic 

 activity not only in the purely chemo-synthetic reactions of the auto- 

 trophic plants, but also those reactions involving photo-chemical 

 changes. From the thermo-dynamic point of view it seems improbable 

 that a synthesis of carbohydrates from carbon dioxid and water would 

 be possible from the energy made available by the reverse process, the 

 combustion of carbohydrates. For further information on this highly 

 important phase of plant energetics, consideration is being given to the 

 energy relations of those organisms which, by means of their metabolic 



