226 CHAP. XXV. PHOTOSYNTHETIC STORAGE OF SOLAR ENERGY 



Table XXXII. 



-Showing Energy-Relation in Photosynthesis of 

 the Leaf of Polygonum Weyrichii 



The accuracy of an estimation of the efficiency of the 

 photosynthetic organ depends on the reliability of the 

 experimental determination of the energy absorbed in 

 photosynthesis. This, it should be remembered, cannot be 

 found directly, but only by subtracting from the amount of 

 incident energy the various losses, none of which can be 

 found with any degree of accuracy. These losses, moreover, 

 are very considerable compared with the calculated value 

 of the absorbed energy. Thus, taking the experiment 

 number 4 in the above Table, we find that, while the pro- 

 portion of energy used in photosynthesis is only 1-32, the 

 various losses are proportionately very much higher, 35 • 64 

 for transpiration and 27-76 for re-radiation and convection. 

 The inevitable errors in the determination of these losses 

 must seriously affect the calculated value of the energy 

 absorbed in photosynthesis, and must thereby introduce 

 considerable error into the determination of the efficiency. 



The estimates hitherto made by different observers agree 

 generally in assigning a very low efficiency to the photo- 

 synthetic organ, of the order of o-6 per cent, or so ; a few, 

 however, ascribed a much higher value to the efficiency. 

 But no great reliance can be placed on these results, since 

 the methods employed were subject to serious shortcomings. 

 First, the period of experiment was necessarily prolonged, 

 so that it was impossible to obtain any accurate measure 



