THE CHEMISTRY OF PHOTOSYNTHESIS 293 



erroneously taken for formaldehyde. It is very doubtful, however, v^hether 

 this compound is in any way associated with photosynthesis, though it is 

 apparently widely distributed. 



3. Feeding Experiments 



Another line of reasoning which has been followed in endeavoring to 

 determine the nature of the intermediate products of photosynthesis is 

 the feeding to the plant of such substances which are supposed to con- 

 stitute intermediate products, and to determine whether such feeding re- 

 sults in an increase in dry weight, of starch or of sugar by the plant. 

 It is essentially a physiological method and exi>eriments along this line 

 have been carried out for a very long time. No decisive results have 

 been obtained by the use of this method nor is it, in fact, to be expected 

 that there would be. The difficulties associated with the use of this 

 method are of a very fundamental nature. In the normal metabolism 

 of an organism, and there is no reason why photosynthesis should form 

 an exception, the products which constitute the intermediate steps in these 

 activities bear a rather definite relation to the needs or capacity for the 

 further transformation of such products. That is, the amount and con- 

 centration of the intermediate products in the normal course of the 

 processes are adjusted to the capacity of the organism to utilize or dis- 

 pose of them. An undue accumulation usually results in rather deep 

 seated disturbances of all the processes of the organism. There is, more- 

 over, good reason for believing that some reactions are carried out in 

 locaHzed areas within the cells ; whether this is due to localization of 

 enzymes, to differences in the pH or to other facts it is unnecessary to 

 dwell on here. That such localizations play a role in photosynthesis 

 the very nature of the chloroplasts would indicate. Finally, the rate at 

 which the intermediate products are supplied to the centers where they 

 are converted, undoubtedly plays a very important role in maintaining 

 the normal course of the reaction. To these circumstances may be added 

 that it is conceivable that in a complex series of reactions, such as photo- 

 synthesis, we are probably not dealing with a single intermediate product, 

 but there exists the possibility that several such products are essential 

 for the reaction, and increasing the concentration of only one may be of 

 little influence on the total reaction or may, in fact, inhibit it. 



In view of these considerations the feeding to a plant of a substance 

 which according to theoretical views may constitute an intermediate prod- 

 uct of photosynthesis has little chance of leading to very definite con- 

 clusions. The difference between the two conditions of the natural forma- 

 tion on the one hand and the artificial feeding on the other becomes 

 evident in the case of formaldehyde. In the normal process, from all 

 we know, at least one important step takes place in the chloroplasts in 

 the cells, and let us assume that here formaldehyde is formed. From 

 the fact that there have been no reliable tests obtained from illuminated 



