VARIATIONS IN RESPIRATORY ACTIVITY IN RELATION 
: TO SUNLIGHT 
H. A. SPOEHR 
(WITH TEN FIGURES) 
Although the importance of light as a physiological stimulus 
and as a climatological factor has long been recognized, the com- 
plexity and multiplicity of biological light reactions has but recently 
been realized. As a working hypothesis, I have endeavored to 
analyze the light reactions by dividing them into two classes: 
(1) those reactions which are brought about by the light directly 
inducing chemical or physical changes of certain physiologically 
important substances within the organism; and (2) those reactions 
which are caused by the light affecting the environment of the 
organism. In the first class fall such reactions as the reduction of 
the acidity of the plant juicest with the consequent effects on growth, 
the inversion of disaccharides, and a number of other purely photo- 
chemical reactions. This paper is a prefatory announcement of a 
reaction which I believe to belong to the second class. It is my 
hope, by means of such an analysis, eventually to be able to inter- 
pret climatological light reactions upon a sound physiological 
basis. 
As one of the most simply measurable plant activities, I have 
chosen respiration, as indicated by the evolution of carbon dioxide. 
The great complexity of the chemistry of this process in no wise 
affects the results for the present purpose. 
The effect of light upon the respiratory activity of living things 
in general has received considerable attention. Unfortunately, 
however, in most of these investigations the source and nature of the 
light used were not considered, and hence we have a mass of unco- 
ordinated and often contradictory results. Im 1855 Mo teEscHotT’ 
* Ricuarps, H. M., Reports in Yearbook Carnegie Inst. Wash. 1913 and 1914- 
Sporur, H. A., Photochemische Vorginge bei der diurnalen Entsdurung der 
Succulenten. Biochem. Zeitschr. 57:95-111. 1913. 
2 Morescuort, Jac., Die internationale Sanitits Konferenz in Rom. 
Med. Wochenschr. 1855. nos. 36-38. 
Botanical Gazette, vol. 59] 
Wiener 
[366 
