64 



STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 



hour of the experiment with the more easily penetrating glj^cocoll 

 and asparagine. With d-levulose no stimulating effect can be 

 noticed in our experiments; in fact the respiration rates in the 

 experiments with glycocoU or asparagine and d-levulose are relatively 

 below those with this sugar alone during the first half of the time. 



6. d-mannose. 



A sugar which is closely related in structure to both d-glucose 

 and d-levulose is d-mannose. These three sugars have a common 

 enol and are easily converted into each other. ^ Aside from its 

 rather common occurrence as an anhydride, mannan, in seed coats 

 and similar organs, the physiological behavior of d-mannose in 

 plants has been investigated very little. Knudson^ found that 

 d-mannose has a decidedly toxic action on the root tips of wheat 

 and peas grown in sterile agar cultures. 



We carried out but two complete experiments with d-mannose, 

 one without and the other with glycocoU in the nutrient solution. 

 The results were quite surprising in that there was no toxic action 

 apparent and that the rates of respiration developed a very great 

 increase over the initial rate. 



In table 46 the analytical data are given representing the changes 

 in material in leaves which have been given d-mannose. 



Table 46. 



The results of the determination of respiration-rates for this experi- 

 ment are given in table 47 and figure 17. 



The foregoing experiment was repeated with the addition of 0.11 

 per cent of glycocoU to the nutrient solution. The analytical data 

 are given in table 48. 



The results of the determination of the respiration rates are com- 

 piled in table 49 and figure 17. 



The experiments with d-mannose are noteworthy on account of 

 the great increase in amino-acids in both cases. Although the 

 petioles of the leaves were standing in a 7 per cent solution of 

 d-mannose, there was a very appreciable decrease in the total sugar- 



1 Spoehh, H. a. The carbohydrate economy of cacti. Carnegie Inst. Wash. Pub. No. 287 



(1919). 



2 Knudbon, L. Amer. Jour, of BoL, 4, 430-437 (1917). 



