10 Lewis Knudson 



and is still receiving much attention from the United States Bureau 

 of Soils. Practically no consideration, however, has been given in this 

 country to the possibility of a favorable influence of dissolved organic 

 matter, although Schreiner (1913) does suggest the direct utilization 

 of organic nitrogenous substances. The relatively recent investigations 

 have proved the ability of the higher plants to directly absorb, by means 

 of their roots, a considerable number of different organic substances 

 present in the nutrient media. This has created a new interest in the 

 role of the organic material of the soil in the nutrition of the higher plants. 



It is of course recognized that the plants may grow and mature in 

 the absence of organic material from the substratum, and it is further- 

 more recognized that in many soils there is such a relatively small amount 

 of organic matter that its significance as a source of carbon would be 

 very slight and perhaps of no direct value.. However, the fact that in 

 many soils a rich microbial flora exists, postulates the presence of directly 

 available organic substances or of substances made available by extra- 

 cellular digestion. Since there is no reason to assume that permeability or 

 metabolism in fungi and bacteria differs fundamentally from that in 

 higher plants, it is logical to conclude that in general what is available 

 for the fungus is likewise available for the higher plant. In this con- 

 nection the fact is significant that there exist among the phanerogams 

 plants devoid of chlorophyll, which necessarily derive all their organic 

 material from the soil. 



Theoretically there is no reason why higher plants should not absorb 

 dissolved organic substances by means of their roots. The results of 

 recent investigations have confirmed the theory. The phanerogamic 

 plants studied have been found capable of absorbing and assimilating 

 a considerable number of organic substances. The practical significance 

 of this fact may be little, but, irrespective of the practical aspect, a thorough 

 knowledge of the relation of the higher plants to dissolved organic sub- 

 stances is desirable and may be important in the interpretation of experi- 

 mental data in other lines of research. Such a knowledge is desirable 

 furthermore from the standpoint of a better understanding of metabolism 

 in plants and because of its significance to animal physiology and 

 biochemistry. 



With a view to confirming and extending the investigations of previous 

 workers, this study was begun in December, 1912, and the work here 



