16 Lewis Knudson 



tends to be chlorotic, a similar observation also being noted by Maze and 

 Perrier (1904) for corn grown with glucose added to the culture solution. 

 The suggestion was made by these authors that there seems to be a dis- 

 appearance of chlorophyll with reduction of its function, although no 

 evidence has been produced to show loss of function. 



Investigations on the role of organic nitrogenous substances have been 

 made largely from the viewpoint of the value of the substance supplied 

 as a source of nitrogen. Lutz (1898), employing cultures free from 

 micro-organisms, succeeded in demonstrating that certain of the amines 

 could serve as sources of nitrogen. Hutchinson and Miller (1911) have 

 extended the investigations of Lutz to other plants with favorable results. 

 These authors have presented a critical survey of the work performed, 

 and make the following statement concerning the previous work: 



As regards organic compounds the great majoritj' have given negative, if not uncertain 

 results. More or less satisfactory^ evidence of assimilation has been obtained with the follow- 

 ing compounds — methyl-, amyl- and allylamines, dimethylamine, acetamide, choline, 

 betaine, leucine, urea, dicyano-diamide, aspartic acid, asparagine, glutamine, allantoin, 

 uric acid, hippuric acid, tyrosine and humic acid. The gains of nitrogen have, however, 

 generally been very small and in many cases negative results have been obtained by other 

 investigators. 



It seems probable that some of the organic nitrogenous substances 

 can supply the needs of the plant, although Russell (1912) is of the opinion 

 that such of these substances as are apparently utilized are split at the 

 surface of the root, yielding ammonia as one product which supplies the 

 nitrogen for the plant. 



As already stated, investigations of the utilization of organic nitrogenous 

 substances have been made largely from the viewpoint of the nitrogen 

 relationships. It is obvious, however, that one cannot entirely dissociate 

 the carbon relationships when experimenting with such substances. 

 It is this viewpoint that has guided Lefevre (1906) in his investigation 

 of the utilization of amino acids in the complete absence of carbon dioxide. 

 Lefevre has apparently demonstrated that certain amino compounds 

 can serve as sources of carbon. He found that Lepidium sativum, Ocimum 

 minimum, and Tropaeolum varians nanum, cultivated in an artificial 

 soil of sand and moss, when grown under a bell jar and supplied with air 

 freed of carbon dioxide, apparently utilized as a source of carbon the 

 amino acids supplied. He used a mixture of tyi'osine, glycocoU, alanine, 

 oxamide, and leucine. Plants grown under these conditions increase 



