1923] 



CAMP — CITRIC ACID AS A SOURCE OF CARBON 281 



ing, making it very difficult to filter off the mat, the supernatant 

 liquid going very slowly through coarse filter paper. 



The curves for the trend of P H are found in fig. 8. Solution 1 

 showed a marked rise of acidity followed by a falling off to alkalin- 

 ity. Solution 2 did not rise in acidity but after 6 days began to 

 fall off steadily toward alkalinity. Whether the development 

 of acid was hindered by the buffer action of solution 2 or merely 

 masked by it is a question that cannot be answered satisfactorily. 

 It is to be seen that as the titer of the solution decreased to a 

 very small amount, utilization of carbon ceased. This might have 

 been due to the fact that the solution was too alkaline for the 

 metabolism of this fungus or that the fungus could not utilize 

 the citrate radical when comb ned with potassium. 



Alternaria Citri and Alternaria sp. — These 2 fungi will be dis- 

 cussed together for the sake of comparison. The solutions con- 

 tained KNOi as a source of nitrogen and 100-cc. flasks were used. 

 In diluting, 2 flasks were made up to 200 cc. The P H of the solu- 

 tion was about 4.7. 



It is difficult to interpret the weight curves for these organisms, 

 as seen in fig. 14. Organism 14 showed more rapid growth than 

 did organism 7, and if the final high figure for solution 1 is taken 



I 



into account would seem to have made a greater total growth on 

 dextrose alone. However, as will be noted, the dextrose had 

 entirely disappeared 16 days before this final high weight was 

 obtained. There are only 2 reasonable explanations of this fact : 

 the first, that this weight is accounted for by the irregularity 

 of growth, and that these 2 particular mats would have weighed 

 as high or higher at an earlier period; the second, that the mats 

 for some reason were insufficiently dried and consequently were 

 somewhat heavier than they should have been. While this last- 

 mentioned explanation seems improbable, since the mats were 

 run in large groups and no other difficulties were encountered, 

 yet it seems wise to disregard such an unusually high weight 

 occurring at this point. With regard to both of these fungi and 

 other fungi of a similar nature there is considerable irregularity 

 in the weights of the mats, presumably due to the slowness of 

 growth, and consequently the greater likelihood of being influ- 

 enced by factors of the environment. It would have been highly 



