362 Mineral Nutrition of Plants 



the so-called "sparing action" of sugar on respiratory destruction of 

 amino acids (27) is in all probability a "replenishment action" instead. 

 These and other data and interpretations will be found in reviews by 

 Nightingale (29, 30), Chibnall (6), and Vickery (54). The writer has 

 depended to a great extent on these and other workers for information 

 of the accomplishments in the field of protein chemistry. 



A brief reference might be made to the question of amino acid 

 synthesis concerning which so little is known. It was possible by means 

 of Aspergillus niger van Tiegh, a fungus, to demonstrate that normal 

 and optimum growth could take place only with a mixture of glutamic 

 acid, proline, and ornithine in the absence of sugar and other nitrogen 

 (46, 4J). The other amino acids, excepting aspartic, were ineffective, 

 whereas malic acid was also usable. The aspartic and malic acids have 

 the same carbon chain. Adoption of a classification of amino acids into 

 three groups has received some measure of verification through the 

 work of Steward and Street (52) and of MacVicar and Burris (26) on 

 the importance of glutamic acid in amino acid synthesis. Stepka, 

 Benson, and Calvin (5/) found serine and alanine formed during 

 photosynthesis to be radioactive, whereas the large quantities of gluta- 

 mic acid elaborated were inactive. Synthesis of straight chain amino 

 acids with 3 and 4 carbon atoms would seem to follow a different path 

 than those with a 5 carbon atom chain according to their data. 



THE DATA OF MINERAL DEFICIENCY 



It is evident in view of the speed and complexity of nitrogen and 

 carbon metabolism in plants that any deficiency of a mineral element 

 participating directly in protein and carbohydrate reactions would be 

 readily indicated through chemical analysis. The same would also be 

 true for an indirect participation, as in enzymes controlling these reac- 

 tions. However, deficiencies drastic enough to influence a basic reaction 

 of protoplasm would affect all physiological processes and could not 

 be accepted as proof of a role in a limited phase of nutrition. 



A feature of mineral nutrition studies that has long puzzled the 

 writer has been the chemical mechanism whereby characteristic defi- 

 ciency symptoms are produced in the plant. Data obtained in aseptic 

 culture with amino acids has indicated the probable participation of 



