DEPARTMENT OF BOTANICAL RESEARCH. 65 



nature of hydrolysis and oxidation. A wealth of knowledge has been 

 gained from the chemical investigations of the products of hydrolysis 

 of the more complex plant products. The most evident chemical pro- 

 cess of living things is, of course, the oxidation of organic food material, 

 and great progress has been made in the chemical interpretation of 

 these oxidation processes. 



But hydrolytic and oxidative changes are by no means the only 

 chemical changes occurring in the living organism. The reverse of these 

 changes are very common and play an exceedingly important role in the 

 general metabolism. Reducing reactions and dehydration and conden- 

 sation syntheses must be taken into consideration in any attempt to inter- 

 pret the phenomena of plant metaboHsm from a chemical basis. These 

 reactions have been very generally neglected by plant physiologists. 

 It is a remarkable fact that in protoplasm (consisting in large propor- 

 tion of water and apparently organized most favorably for union with 

 oxygen) chemical changes may take place involving the liberation of 

 water which can be duplicated outside of the cell only by means of high 

 temperature or by strong water-attracting substances; and similarly 

 in protoplasm there occur reducing actions involving a high reduction 

 potential. From chemical and physiological considerations there is 

 reason to beheve that many of the dehydration and condensation syn- 

 theses are produced not by simple taking out of water but by reduction 

 followed by condensation and possibly oxidation. Very few such re- 

 actions have, however, as yet been produced outside the living cell. 



A question of the greatest theoretical as well as practical interest 

 is the manner in which the energy is obtained for these reducing and 

 dehydrating changes, for such changes always involve an increase in 

 the potential energy of the substances formed. It is now recognized 

 that, just as in the case of the reduction reaction of the photosyntheti- 

 cally active leaf already noted in the annual report, these reductions 

 and dehydrations are retarded if the respiratory activity of the plant 

 is reduced. 



Of all the substances found in plants the sugars command the center 

 of attention in considering the various aspects of plant metabolism. 

 All evidence points to the conclusion that sugars are the first products 

 which accumulate in the process of photosynthesis, and they thus form 

 the starting-point for the synthesis of the tremendous number of sub- 

 stances found in plants. As nothing is known as to how these reduc- 

 duction and dehydration actions proceed in the plant, it is essential to 

 gain some purely chemical information regarding the processes. Theo- 

 retically it should be possible to produce synthetically some of the most 

 valuable plant products. Experimental investigations in this field 

 were not pursued on account of the high cost of original raw materials. 

 Recently abundant new sources have been found from which such 

 material can be gained very readily. The most promising starting- 

 point is the five-carbon atom or pentose sugar. 



