172 PLANT PHYSIOLOGY 



disputed point. If we compare the structure of glucose with that 

 of the amino acid, lysine, a marked similarity is observed. 



HHHHH HHHHH 



H— C— C— C— C— C— C=0 H— C— C— C— C— C— C=0 



OH OH OH OH OH H NH 2 H H H NH 2 OH 



glucose lysine 



After the glucose was once changed to a fatty acid, the difficul- 

 ties of which were considered in the last chapter, the change to 

 the amino acid would not be so hard to accomplish. It has been 

 thought for some time that the plant combined the nitrogen from 

 nitrates with the transformed carbohydrate and thus produced the 

 amino acid. It was even thought that this might be dependent 

 upon light since proteins are made ordinarily only in the presence 

 of light. In the dark, nitrates collect in the plant, but disappear 

 in the light. Zaleski and Suzuki (1897-1901) showed, however, 

 that if sunflower leaves were floated upon a solution of sugar and 

 nitrate, much protein was manufactured even in the dark. Palladin 

 (1899) obtained similar results with bean leaves, but even here 

 more protein was manufactured in the light. Leaves which 

 contained 18.6 g. of protein when gathered, contained 67.2 g. 

 at the end of six days in the dark on a sugar solution, and 140.9 g. 

 in the light. The light, however, seems necessary chiefly for the 

 production of the preliminary carbohydrates, which explains why 

 the nitrates collect in the plant in the dark. If plenty of carbo- 

 hydrates are available from outside, as in the experiments of 

 Zaleski and Suzuki, the protein manufacture will continue in the 

 dark. 



In the laboratory, amino acids have been synthesized by the 

 action of ammonia on glyoxylic and sorbic acids, both of which 

 are found in plants and may be obtained from the oxidation of 

 simple sugars. Does the plant use this same method? The answer 

 is doubtful. 



It has been suggested that the light plays a prominent part in 

 the synthesis of proteins not only in the manufacture of carbohy- 

 drates but in the transformation of nitrogen from the nitrate into 

 the amino form. From this angle the problem was attacked by 

 Baudisch (1911-1918) who found that when a mixture of potas- 

 sium nitrite and methyl alcohol in water was exposed to ultra- 



