78 CARNEGIE INSTITUTION OF WASHINGTON. 



An instrument was attached to a sycamore {Platanus occidentalis) 

 in the grounds of the Missouri Botanical Garden, under the care of 

 Dr. Hermann von Schrenk and associates, in March 1918. This 

 observation was interrupted several times and the yoke was changed 

 to one of bario in April. When a satisfactory adjustment had been 

 obtained on May 5, enlargement was in progress and continued through 

 all records up to September. 



METABOLISM AND NUTRITION. 



The Interrelation of Photosynthesis and Respiration, by H. A. Spoehr and 



Frances Long. 



A question on which there has always been a great deal of specula- 

 tion and controversy is whether photosynthesis is a process intimately 

 associated with the vital activity of the plant and thus dependent upon 

 the general protoplasmic metabolism, or whether photosynthesis is an 

 activity which proceeds more or less independently of these functions, 

 contributing the material necessary for the release of energy and 

 growth, but independent of metabolic activity. There is no definite 

 experimental evidence applicable to this question, which is of prime 

 importance in the interpretation of existing data, as well as for de- 

 termining the direction of subsequent investigation. If such a direct 

 interdependence exists, it is to be expected that factors influencing 

 respiration would then also affect the photosynthetic activity. For 

 this reason a comprehensive investigation of respiratory activity of 

 leaves was also undertaken. There are, of course, a number of factors 

 which work together to determine the rate at which carbon dioxid is 

 emitted by the mature leaf. The most immediate of these for the 

 present consideration is the supply of carbohydrates. As the store of 

 carbohydrates in the leaf becomes reduced, the rate of respiratory 

 activity exhibits a decided decrease. From such data as is available 

 now, it may be inferred that a reduced respiratory activity represents 

 also a lowered energy release. Were there, then, an intimate relation 

 between the photosynthetic activity and the metabolism of a leaf, 

 corresponding difTerences in the rate of carbon-dioxid fixation should 

 appear under conditions of active and reduced respiratory activity as 

 affected by the supply of carbohydrates. 



An extensive series of experiments was inaugurated to determine 

 the rate of photosynthesis of isolated leaves in various stages of car- 

 bohydrate depletion. These may be summarized to the effect that 

 leaves exhibiting high respiratory activity show a correspondingly 

 high photosynthetic activity, while leaves which are respiring at a 

 low rate also fix carbon dioxid slowly. There are, of course, upper and 

 lower extremes, where the rule is altered, owing to the introduction 

 of other disturbing factors. That this is not due to the varying amounts 

 of carbon dioxid available to the plant was established by the use of 



