DEPARTMENT OF BOTANICAL RESEARCH. 61 



of this metabolism and of the varjdng sugar-content of the leaf on 

 photosynthesis. The role in respiration and photosynthesis of the 

 proteins, amines, and amino-acids is being studied in the light of their 

 regulatory and catalytic properties as components of protoplasm. And 

 finally, the effect of the inorganic nutrients on photosynthesis is being 

 investigated with a view of gaining some light on the role of these 

 substances and estabUshing a rational basis for the use of mineral 

 salts in relation to respiration and photosynthesis. 



It has become e\'ident that enormous differences exist in the leaves 

 of different species as to the rate of carbohydrate elaboration and 

 consumption. For example, leaves of Helianthus and Phaseolus, 

 which with the comparative method of the iodine test show about the 

 same rate of starch formation and consimiption, when more carefully 

 examined exhibit great differences. The former is about ten times 

 more active than the latter, both as to respiration and as to photo- 

 synthetic activity. In general, it v/ould seem that these two processes 

 run at parallel rates, i. e., plants which form carbohydrates rapidly 

 also show a high rate of depletion of stored material. In the cacti 

 and other plants rich in carbohydrates it has already been found 

 that an increase in carbohydrates above certain limits does not result 

 in increased carbon-dioxide evolution. Similarly, with decreasing 

 carbohydrate supply, the rate of carbon-dioxide emission reaches a 

 lower limit, below which it falls only very slowly. 



From the results so far obtained it appears that the rate of photo- 

 synthesis is also closely related to the sugar-content and to the respira- 

 tory activity of the leaf. 



A leaf in which the carbohydrate supply has been greatly depleted, 

 when first exposed to light, exhibits a low rate of carbon-dioxide 

 fixation. With continued illumination this rate increases decidedly, 

 as does also the rate of carbon-dioxide elimination in the dark. As 

 photosynthesis progresses and the leaf accumulates an abundance of 

 carbohydrates, the rate of carbon-dioxide fixation again decreases. 

 The latter observation is quite in accord with the results of Saposnikow, 

 who demonstrated the reduced rate of carbohydrate formation as 

 these substances accumulate in the leaf. 



The Carbohydrate Economy of Cadi, hy H. A. Spoehr. 



The carbohydrate economy has been followed through a third year, 

 and the seasonal variations analyzed in the light of climatic factors. 

 As a final series of analj'sis, the past year was of especial interest on 

 account of the rather extreme conditions which prevailed. There 

 was very Uttle rainfall during the autumn and winter. The effect 

 upon the carbohydrates of the cacti of these conditions, together with 

 the relatively low temperatures of the early winter, was very instructive. 



