THE ZOOCHLORELL/E OF FRONTONIA LEUCAS. 83 



chlorellse, desmids, and diatoms preceding death only by a few 

 moments. The organisms which contained no zoochlorellse often 

 lived several hours. In fresh spring water specimens with zoo- 

 chlorellse lived from five to eight days. Specimens without 

 zoochlorellse lived indefinitely. In one per cent, dextrose speci- 

 mens with zoochlorellse lived eight days or more. Specimens 

 without zoochlorellse averaged two days. It was found also 

 that if the cultures in one per cent, dextrose were placed in fresh 

 media daily, specimens with zoochlorellse lived indefinitely, 

 while those without lived four or five days. 



Experiments begun June 24, 1926, showed that Frontonia 

 with abundant zoochlorellse may be induced to live several 

 days in a three per cent, solution of dextrose by beginning at 

 one half per cent., changing the medium daily, and increasing 

 the concentration one half per cent, every fourth day. But 

 under no condition have specimens without zoochlorellse been 

 induced to live more than a few hours in a medium exceeding 

 one per cent. 



In two cultures containing one per cent, dextrose vegetative 

 reproduction was observed in Frontonia harboring zoochlorellse 

 where fermentation had been going on three and four days. 

 Frontonia without zoochlorellse would not live in a medium of 

 this kind. 



These observations suggest that specimens harboring zoo- 

 chlorellse are more resistant to media of greater osmotic pressure 

 than are free specimens. 



HYDROGEN ION CONCENTRATION. 



It has been observed that as fermentation progresses in 

 dextrose cultures the hydrogen ion concentration increases; e.g., 

 a one per cent, solution with a pH value of 7.2 made July 18 

 showed, 24 hours later, a pH of 7.1. After 48 hours the pH 

 was 7.0, after 72 hours 6.9, and on the fourth day it had become 

 6.7. Observations made on one, two, and three per cent, solu- 

 tions showed similar increases in hydrogen ion concentration 

 during fermentation. 



The hydrogen ion concentration of media from natural col- 

 lections was then studied. Data gathered from this study are 

 given in Table I. 



