THE ENERGY RELATIONS IN PHOTOSYNTHESIS 323 



Relatively, the amount of energy liberated through the respiratory 

 activity is small. Brown and Escombe calculate for a leaf of H elianthus 

 aiinims, emitting 0.70 cc. carbon dioxide per square decimeter of leaf- 

 lamina per hour, 0.000582 calorie per sq. cm. jjer minute would be evolved, 

 and since the weight of a sq. cm. of this leaf is 0.020 gram, with a specific 

 heat of 0.879, the heat of respiration would raise the temperature of the 

 leaf at the rate of 0.°033 per minute, assuming that the leaf was not 

 losing heat in any way. 



From the results of Brown and Escombe it is apparent that the en- 

 ergy used in photosynthesis varies considerably. In Table 36 are given 

 the results of some of their experiments. Simultaneous experiments 

 were carried out in which all conditions were kept the same except the 

 insolation, R. In one case. A, the leaf was exposed to full insolation ; 

 in the other case, B, only a portion of that used in A was allowed to 

 fall on the leaf ; revolving sectors were used to reduce the insolation. 

 It was attempted thus to alter but one factor, that of light intensity. 



TABLE 36 



Disposal of Energy Incident on a Leaf. The Total Energy Received by the 



Leaf Is Taken to Equal 100. (From data of Browne and Escombe.) Nos. 1 



to 8 Are for Hclianthus annus, with a Coefficient of Absorption, a, of 



0.686, and 9 to 11 for Scnecio grandif alius with a of 0.744. R Is 



Given in Calories per Sq. Cm. of Leaf Lamina per Minute. 



