8o 



Journal of Agricultural Research 



Vol. XIX, No. a 



A brief consideration of the results obtained in this series shows them 

 to be abnormal, since one would scarcely expect the decided drop in growth 

 in cultures 4, 5, and 6 if reaction were the only factor concerned. The 

 fact that there developed a decided opalescent or colloidal appearance 

 in these cultures in about 24 hours after their renewal, together with the 

 fact that there was a large decrease in acidity during the 4 days ' growth 

 of seedlings indicated that they were infected with some bacterial organ- 

 ism which evidently used the citric acid present as a source of energy. 

 Microscopic examination of these solutions showed this to be the case, 

 and it was at once surmised that the depressant effect of these solutions 

 upon the growth of wheat seedlings was probably due to the assimilation 

 of the nitrates by these bacteria. This hypothesis was substantiated 

 by a determination of nitrates in all seven cultures at the end of a 4-day 

 period. The relative total green weights of seedlings, based upon the 

 highest taken as 100, the relative nitrate content, based upon the highest 

 taken as 100, and the relative decrease in acidity of the solutions, based 

 upon the greatest decrease taken as 100, are shown in Table III. The 

 relation of the change in reaction taking place in the 4-day period to the 

 original reaction of the solution is shown graphically in figure i,B. 



Table III- — Comparative total green weights, nitrate content, and acidity of cultures of 

 series A at end of 4-day period 



Solution No. 



I. 

 2. 



3- 

 4- 

 5- 

 6. 



7- 



The data show that depression in growth in cultures 4, 5, and 6 is 

 associated with low amounts of nitrates left in solution and with large 

 decrease in acidity. It seems safe, therefore, to conclude that the bacteria 

 present were responsible for the abnormal effects obtained in this series. 

 It should be noted that although there was more citric acid available to 

 the bacteria in culture No. 3 than in No, 4, there was actually much 

 smaller assimilation of nitrates in the former culture, while the wheat 

 growth in No. 3 was almost equal to that in the best member of the series. 

 Apparently the acidity of this culture has suppressed the growth of the 

 nitrate-assimilating bacteria but has not had a correspondingly unfavor- 

 able effect on the growth of wheat seedlings. Since there was little dif- 

 ference in the amounts of nitrates present in cultures 1,2, and 3 it seems 



