THE CHEMISTRY OF PHOTOSYNTHESIS 257 



it is daily before the eyes of every one, it is a rather remarkable fact that 

 there have been no chemical investigations embodying a sustained and 

 persistent effort. There have been no long continued investigations such 

 as characterize the work of Fischer on the carbohydrates and the proteins, 

 of the Curies on radioactivity or Richards on atomic weights. The reason 

 for this may lie in the fact that the problem is an exceedingly difficult one, 

 and that the research work did not yield results as readily as in other less 

 complicated fields. 



Among the features of the photosynthesis problem which make a care- 

 ful theoretical analysis of the reactions a difficult task are the following. 

 First of all, it is in part at least a photochemical reaction. There is as 

 yet very little known regarding the mechanism of photochemical reactions. 

 We have no law for the eft'ect of radiant energy corresponding to Faraday's 

 law for the effect of electrical energy. Moreover, photosynthesis is an 

 endothermal reaction. There are no analogous reactions known, reactions 

 in which there is a storing of energy approaching in amount that taking 

 place in photosynthesis. The role of chlorophyll is still not clearly 

 understood. 



There is in photosynthesis a great increase in potential energy between 

 carbonic acid and glucose. It is possible to conceive of a number of ways 

 in which this change can take place and the efforts of the chemists have 

 to a large extent been devoted to devising theories to account for the steps 

 between carbonic acid and glucose. One difficulty has been that some 

 of these theories are not amenable to test by means of experimentation 

 on the living plant or only to a very limited degree. Moreover, many of 

 the theories have been formulated with almost complete disregard of well 

 founded physiological facts. 



Probably the most difficult point is that photosynthesis is closely asso- 

 ciated with, in fact, is apparently dependent upon the life activities of the 

 plant. Attempts to define more closely the relationship between photo- 

 synthesis and the activity of the plasma have not been very successful. 

 The idea that there exists such a relationship is based upon the inactivation 

 experiments of Ewart, the fatigue phenomena of Pantanelli and similar 

 experimental observations which have already been discussed. Similarly, 

 Willstatter and Stoll, after greatly advancing our knowledge regarding 

 the role of chlorophyll, come to the conclusion that the rate of photo- 

 synthesis is to a large measure controlled by the activity of an enzyme. 

 This idea was not new, but has found considerable supi^rt in the experi- 

 mental results of Willstatter and Stoll. These are based largely upon 

 differences in the temperature coefficient with changes in external condi- 

 tions and in chlorophyll content. Direct evidence of the participation of 

 an enzyme is still wanting. 



The complexity of the chloroplasts, which are undoubtedly the centers 

 of photosynthetic activity, adds to the difficulty of the problem. Whether 

 we are dealing here with surface phenomena and pressures is a problem 

 regarding which we have hardly any information. The failure to accom- 



