[Vol 10 



356 



ANNALS OF THE MISSOUKI BOTANICAL GARDEN 



fall noted was not brought out by the first series with this fungus 

 because determinations were not made until the third day of 

 incubation. A possible explanation is similar to that offered for 

 the action of the organism on the P— medium. The period of 

 spore germination and extension of the young germ tubes is one 

 in which the nitrogen of the KN0» is more rapidly used than is 

 the dextrose decomposed to form organic acids, and consequently, 

 due to the freed K, there is a slight increase of the hydroxyl 

 ions above the original hydroxyl-ion content of the medium. 



KNOi 



• * 



Fig. 16. Total N io 50 ml. media. Aspergillus niger, first series. 



This is followed by the short period of the predominance of organic 

 acids from the decomposed dextrose and the resulting increase in 

 acidity. Then after the fifth day, the sugar and organic acids 

 being nearly all assimilated, the increasing products of autolysis 

 plus the OH resulting from the different rates of assimilation of 

 the potassium and nitrate ions from the KNO», the K being in 

 excess of the needs of the fungus, rapidly change the reaction 

 toward the alkaline side. In the cultures of the slower- growing 

 DiplodiaandSphaeropsis the above phenomenon is not in evidence. 

 The medium was gradually diminished in acidity from P H 4.0, 

 becoming strongly alkaline (P H 7.8 in the Diplodia cultures and 

 P H 8.1 in the Sphaeropsis cultures). Up to the twelfth day for 





