174 PLANT PHYSIOLOGY 



synthesis is dependent upon light only for the formation of the 

 active formaldehyde, (2) part of the formaldehyde is used for 

 making proteins and part for the carbohydrates as described in 

 Chapter VI, and (3) part of the formhydroxamic acid is used also 

 for making the nitrogen bases and the alkaloids, both of which 

 are considered to be waste products. This entire scheme may be 

 represented by the following diagram-summary: 



formaldehyde 

 carbohydrates \ + nitrates 



formhydroxamic acid 

 N-bases alpha amino acids 



alkaloids 



substituted amino acids, 

 e. g., histidine 



Proteins. 



The chief objections to this work of Baly are that (1) it is based 

 entirely upon work in vitro, and (2) it has been shown rather 

 conclusively that light is not necessary for the synthesis of proteins 

 aside from the question of the carbohydrate supply. 



The main steps in the general process are now fairly well agreed 

 upon. The nitrates, as stated above, are combined with carbo- 

 hydrates or their derivatives to form the amino acids, which are 

 then combined into proteins. It is a curious fact that although 

 most plants can use nitrates better than ammonium compounds 

 (Chap. IX), the plant must first transform the nitrates into nitrites 

 and then into ammonia by the aid of reducing enzymes called 

 reducases (Eckerson) in order to produce the amino form of 

 nitrogen necessary for the production of amino acids. 



Animals are rather reckless in their use of proteins. Since they 

 get their supply of this element from the outside by feeding on 

 inferior forms, they have not been forced to conserve their nitrogen 

 supply as have plants. The result is that large amounts of nitrog- 

 enous wastes are excreted daily in the form of urea. Plants do 

 not excrete nitrogen in this fashion but use the same materials 



