[Vol. 10 



254 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



accounts for growth over certain fixed periods is absolutely 

 comparative — only growth curves plotted from frequent deter- 

 minations can be truly comparative. 



Use of varying amounts of citric acid. — Using peptone as a source 

 of nitrogen a large series was run, using varying percentages of 

 citric acid-potassium citrate mixture. The solution used was 

 based on analyses of oranges and lemons given by various authors. 

 Using M/10 MgSO< and M/5 KHJXX, the following solution 

 was used: KH,PO«, 300 cc; MgSO,, 30 cc; peptone, 30 gms.; 

 dextrose, 15 gms.; M/1000 FePO«, trace; distilled H,0 to make 

 1 liter. This was diluted to make V/i liters, this dilution allowing 

 for the addition of the citric acid mixture. The citric acid solution 

 contained 0.25 gm. per cc. and the P H was adjusted by the use 

 of a solution of potassium citrate equivalent to the acid solution 

 in citrate ion. Using varying amounts of the citric acid and potas- 

 sium citrate solution, titration curves were made for solutions 

 containing 2^j and 5 per cent of the citrate radical; and another 

 series of curves was constructed for the titration of the culture 

 solution with citric and hydrochloric acids. From these data 

 solutions were made up to P H 3.0 and 4.5, using 3 different con- 

 centrations of acid, that is, 2J^ and 5 per cent citric acid (citrate 

 radical), just sufficient citric acid to obtain the desired P H , and a 

 check solution with just enough ITC1 to obtain the desired hydro- 

 gen-ion concentration. The fungi were grown in triplicate in 2 

 temperatures, that is, 18-20° C. and 30° C. At the end of varying 

 periods, depending on the speed with which the fungus grew, the 

 weights of the mats and the P H of the culture solution were deter- 

 mined. The concentration of the dextrose was rather small 

 (10 gms. per liter), and the fungi were dependent ehiefly upon 

 the citrate-citric acid mixture for carbonaceous material. The 

 results are given in table x, the weights representing averages of 

 triplicate cultures. 



In considering the results shown in table x certain factors in 



regard to the solution must be kept in mind. The weights for 

 the HC1 blanks probably do not represent the maximum weight 

 attained, the maximum in most instances probably coming before 

 the cultures were taken down. This loss of weight by autolysis 

 was probably not very great in any case except in that of Sclero- 



