80 STUDIES IN PLANT BESPIRATION AND PHOTOSYNTHESIS. 



to respiration, that as photosynthesis proceeds the rate of respiration 

 increases. It would appear, then, that the amount of radiant energy 

 utiHzed in the photosynthetic process decreases as photosynthesis 

 proceeds, and the plant's internal-energy release presumably increases, 

 due to higher respiratory activity from the greater available car- 

 bohydrate-supply. 



That a general relationship exists in leaves between the rate of 

 carbohydrate synthesis and consumption has been recognized for 

 a long time.^ Boysen-Jensen^ summarizes his studies as follows: 



"In Sinapis the intensity of the CO2 assimilation is very great, rising to at least 

 6 mg. CO2 per 50 cm.^ per hour at 20°. Also respiration in the leaves is great, about 

 8 mg. CO2 per 50 cm." per hour at 20°. The point of equilibrium between CO2 

 assimilation and respiration lies at a light intensity of 1.0 (Bunsen units XlOO). 

 The development of a Sinapis plant is very weak. In 44 weeks the dry-matter con- 

 tent rises from 0.5 gram to 38 grams per 100 of plant. In favorable conditions the 

 daily percentage production of dry matter can be estimated as about 15. 



"In Oxalis the maximal intensity of CO2 assimilation is very small, about 0.8 

 mg. CO2 per cm.^ per hour at 20°. Also respiration of the leaves is very small, about 

 0.1 to 0.2 mg. CO2 per 50 cm.^ per hour at 20°. The point of equilibrium between 

 CO2 assimilation and respiration lies at a light intensity of 0.2. The daily produc- 

 tion of dry matter is at 2.1." 



If an actual chemical or energetic relationship exists between 

 the photosynthetic and respiratory activities of the leaf it should be 

 expected that any disturbance in the respiratory activity would be 

 reflected in photosynthesis. The observations on the effect of re- 

 duced oxygen pressure and of narcotics on photosynthesis are of 

 special interest in this connection, Boussingault^ and Pringsheim* 

 investigated the effect of lack of oxygen on the rate of photosynthesis 

 and concluded that it is inhibited thereby. Willstaetter and Stoll,^ 

 from their extensive experiments decide that oxygen is absolutely 

 necessary for the photosynthetic reaction, but that very small 

 amounts of oxygen suffice. This small amount of oxygen, they 

 claim, need not be present as free oxygen, but as loosely bound, 

 "dissoziabel gebundener." Although their experiments were appar- 

 ently carried out with great care, it is a question whether they 

 succeeded in removing all the oxygen which is occluded in the leaves. 

 This fact, however, stands out clearly in their experiments, that the 

 more perfectly the oxygen has been removed the greater is the 

 inhibition of the photosynthetic activity. Also, leaves which had 

 been previously kept in the dark and their carbohydrate-content 

 thus reduced showed no photosynthesis in an atmosphere freed from 

 oxygen. From these experiments it appears that leaves with low 



1 EcKERSON, S. Bot. Gaz., 48, 224-228 (1909). 



2 Botsen-Jensen, p. Botanisk Tidsskrift, 36, 21&-259 (1918). 

 ' B0US8INGAULT, J. B. Compt. rend., 61, 608 (1865). 



* Pringsheim, N. Sitzber. der Preus. Akad. der Wias., 763 (1887). 



• Willstaetter, R., and A. Stoll. I. c, 344r-370. 



