



1923] 



CAMP — CITRIC ACID AS A SOURCE OF CARBON 261 



a Penicillium or of Alternaria Cilri was more than the blank. 

 Sclerotinia Libertiana produced acid in the presence of NH4NO1 

 but not in the presence of the other nitrogen sources. 



In utilizing free citric acid the 2 species of Penicillium and 

 Aspergillus sp. were undoubtedly most efficient. On blanks of 

 about 170 cc. of N/10 NaOH the readings for these fungi, even 

 after the short period of 5 days, were in the neighborhood of 5 

 cc. of N/10 NaOH or less. It is difficult to decide whether the 

 source of nitrogen had any effect on the destruction of the acid, 

 the case of organism 3 over the 5-day period being the only one 

 which gives any indications (NH 4 NOi seemed in this case a 

 little less efficient than the other nitrogen sources). Alternaria 

 Citri failed to survive the treatment with citric acid. There was 

 an indication that some acid was used in the 9-day period but 

 the amount was so small that possibly the very thick and spongy 

 mat may have held back sufficient acid in washing to account 

 for the loss. In the case of Sclerotinia Libertiana and Diplodia 

 natalensis the figures would indicate that there was greater use 

 of citric acid in the second period of 5 days than in the first period 

 of 9 days. This may be due to the increased growth of the mat, 

 resulting in greater absorbing surface. It would hardly be safe 

 to attribute it to "acclimatization" of the fungus to this acid 

 environment, although this might be the case. It will be noted 

 that in the course of changing the solutions the original solution 

 was made up with KNOi. The first change was to a sugar solution 

 with NH 4 NO, and KNO, as nitrogen sources, while at the next 

 change the same nitrogen sources were retained for these 2 mats. 

 In both cases these mats were apparently dead or nearly so when 

 the NH 4 NO»-citric acid solution was removed, nor did the mat 

 revive and show growth when the second sugar solution was added. 

 Peculiarly enough, when the NH<NO,-citric acid mixture was 

 added to another mat on the second round, that is, the mat which 

 had received the Ca(NO0i-citric acid mixture on the first round, 

 the usage of citric acid was practically as good in the case of 

 Diplodia as with the Ca(NOi), -citric acid solution, and in the 

 case of Sclerotinia Libertiana a little better. Just how such data 

 could be properly interpreted is a question. 



Having obtained from the foregoing experiments sufficient 



