336 PHOTOSYNTHESIS 



of low frequency ^^ it is more conceivable how this would be of value to 

 the photochemical process than the heat per se. Although these theoretical 

 considerations are still to be tested by much experimental work, they are 

 not without interest in the light of the results claimed by Detlefsen and 

 by Puriewitsch which have already been discussed. 



Results of the efficiency of photosynthesis somewhat different from 

 those of Warburg and Negelein have been obtained by Wurmser.^* He 

 concludes that Ulva lactuca shows a photosynthetic efficiency in red light, 

 590-700 [i\i, of 59 per cent and in green light 490-590 \i\x, of 83 per cent. 

 Wurmser had previously found a high value of photosynthetic efficiency 

 in the green portion of the spectrum and considers that this maximum 

 efficiency in the green is due to the role which the colorless portion of the 

 protoplasm plays in photosynthesis. He is of the opinion that the libera- 

 tion of oxygen cannot take place in the presence of chlorophyll, for this 

 is very sensitive to photooxidation. Wurmser considers that the method 

 of Warburg and Negelein gave values which are too low for the portions 

 of the spectrum which are feebly absorbed, as the green. It should be 

 stated that Warburg and Negelein did not put particular value on their 

 determinations in this portion of the spectrum. Wurmser also considers 

 that Warburg and Negelein's results in the blue-violet region are too high 

 because of the absorption of pigments other than chlorophyll. According 

 to Wurmser, neither his results nor those of Warburg and Negelein repre- 

 sent the maximum efficiency obtainable in the red. He is of the opinion 

 that the efficiency is practically the same for all wave lengths and probably 

 in the neighborhood of 70 to 80 per cent. 



2. The Storing of Energy by Crop Plants 



In the previous section the question has been discussed what proportion 

 of the radiant energy absorbed by the chlorophyllous portions of a plant 

 are utilized in photosynthesis. In the earlier experiments, this was based 

 upon total solar radiation incident on a leaf, while in the later, more refined 

 experiments, the source of light was confined to a portion of the spectrum. 

 ■As a practical matter, it would be desirable to know what portion of the 

 total energy of solar radiation, falling on an area of land under cultivation, 

 is transformed into the potential chemical energy of the material consti- 

 tuting the body of the plant. 



That this is not an easy matter to determine hardly needs emphasis. 

 Nor can such a determination be taken as a measure of the photosynthetic 

 efficiency of the plants. The growth and development of a plant depend 

 upon a number of factors, of these, the formation of substances formed 

 in the photosynthetic process, is but one. Putter ^^ has endeavored to 



"* Becking, L. B., "Radiation and Vital Phenomena," Dissertation, Utrecht, 1921. 



** Wurmser, Ann. de Physiol. Physiochim. Bio., 1, 47 (1925) ; Compt. rend. Sac. 

 Biol., 83, 437 (1920) ; Bull. Soc. Chim. bio!., 6, 487 (1923). 



""Piitter Die Natimrisscnschaftcn, 2, 169 (1914). Mayer, Landw. Versuchsstat., 

 40, 205 (1892). 



