[Vol. 10 



262 ANNALS OF THE MISSOUKI BOTANICAL GARDEN 



data to give a general understanding of the reactions of the 

 various fungi, it seemed desirable to round out the work with 

 a careful analytical study of their reactions to citric acid. For 

 such a study it was desirable to compare a solution which con- 

 tained only a sugar as a source of carbon with one containing 

 citric acid in addition to the sugar. Growth data covering fixed 

 periods were considered inadequate for such a study and analyses 

 of the culture solution were resorted to. Such analyses and the 

 weights of the mats were taken at frequent periods during the 

 course of growth and curves were plotted from the data so ob- 

 tained. This method gave a complete outline for comparison 

 of the 2 solutions and obviated the difficulties due to variations 

 in the periods of growth in the 2 solutions. 



The culture solution developed by Dr. Duggar and described 

 previously in this article was utilized in this part of the work. 

 Had there been time available for extended comparative work 

 it is probable that a more satisfactory solution could have been 

 found for any one of the fungi or perhaps for the entire group. 

 However, the solution used appeared to be well adapted to the 

 group of fungi as a whole. Wherever possible KNOi was used 

 as a source of nitrogen, since it simplified the analytical work; 

 some of the fungi, however, required peptone, and for Diplodia 

 NH 4 NOi was used. Dextrose was used as the source of carbon 

 since it was easily determined quantitatively and had given good 

 results previously. The citric acid used was Merck 's " Reagent, " 

 and the KOH and potassium citrate Merck's "Highest Purity." 



The question of what cation to use in the partial neutralization 

 of the citric acid was a difficult one. Ammonium citrate gave 

 growth with all the fungi as both a nitrogen and supplementary 

 carbon source, when used with a small amount of dextrose, but 

 the NH« radical complicated the solution unnecessarily and was 

 probably not an efficient source of nitrogen for most of the fungi. 

 Sodium would probably have been satisfactory in many instances 

 but its exact status in relation to the growth of fungi is unsettled 

 and, at least in some instances, it appears to be toxic. Calcium 

 precipitates an insoluble salt with citric acid on heating, and 

 even if Ca(NOi)» is added to the solution after sterilization 

 calcium citrate is precipitated out as soon as the fungus starts 



