STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 



39 



The course of the changes of material was followed by placing 

 five vigorous potted Helianthus plants in the dark at 20° and every 

 24 hours cutting 10 to 12 leaves, which were then analyzed. After 

 the plants had been in the dark for 96 hours they were again placed 

 in sunlight in the greenhouse for 4 hours and another sample of 

 leaves analyzed. The results are given in table 12. 



Table 11. — Rate of CO2 emission of 15 leaves of "Canada Wonder'^ bean at S4°. 

 Petioles in nutrient solution containing no organic substances. 



The analyses given in table 12 indicate a gradual depletion of the 

 carbohydrates available to the leaves when the plants are left in the 

 dark. This depletion can not be made up entirely by drawing upon 

 the reserve material in other parts of the plant. In spite of this 

 depletion it is noteworthy, as has been pointed out, that the rate of 

 respiration of the entire plant rises and then decreases slowly, as is 



Table 12. — Analysis of leaves of Helianthus annuus, after exposure to 

 light, then in dark for 96 hours, and again in light for 4 hours. 



shown in figure 7. After 4 hours of photosynthetic work the leaves 

 have again accumulated considerable sugar. The amino-acids, 

 however, increase in the dark and after subsequent exposure of the 

 plant to light again decrease. 



In table 13 are given the results of plants similarly treated in 

 which the leaves, stems, and roots were analyzed separately. Two 



