Vitamin and Amino Acid Requirements for the 

 Growth of Higher Plants 



WILLIAM J. ROBBINS 



Vitamins 



ONE of the difficulties in discussing the vitamin requirements of 

 higher plants is to define the term vitamin, and to dehmit the 

 substances to be considered. 



In the authorized English translation of the second German edition 

 of his book on vitamins, Funk (15) approved Willaman's (62) definition 

 which is as follows: "\^itamins constitute a class of substances, the 

 individuals of which are necessary for the normal metabolism of certain 

 living organisms but which do not contribute to the mineral, nitrogen 

 or energy factors of the nutrition of these organisms." This definition 

 might be interpreted to include any organic substance which has the 

 following characteristics: it is an essential metabolite, it functions in 

 some other way than as a source of energy or as a major constituent of 

 the plant or animal body, and some individual organism must be supplied 

 with it from without for normal function and development. 



Although by usage the word vitamin has special connotations which 

 limit its application to a more or less well-defined group of substances, 

 the distinction between vitamins, hormones, auxins, growth substances, 

 and cofactors, has tended to disappear. With some exceptions the dis- 

 tinction between the vitamins required by animals and those required 

 by plants has also become less marked. In fact, it is preferable to consider 

 growth requirements from the standpoint of essential metabolites rather 

 than to limit consideration to vitamins, amino acids, purine and pyri- 

 midine bases, or any other particular group of substances. Students of 

 the growth requirements of any group of plants find it advantageous 



