F. G. GUSTAFSON 621 



tion remained constant for 20 minutes it would keep this rate for 

 hours provided food was supplied.) After a constant rate had been 

 established, the material was transferred to the alkaline solution and 

 the rate again determined by noting the time required to produce an 

 equal amount of CO2; i.e., to change from pH 8.92 to 8.68. 



The pH of the nutrient solution both before the spores were sown 

 and after the mycelium had grown large enough to be used was found 

 to be about 4. In no case was there an}^ noticeable change during 

 the growth. A few cultures were grown in a nutrient solution having 

 a pH of 6 to 7. These cultures showed no difference in their behavior 

 from those grown in a more acid medium. The medium on which 

 the fungus was originally growing had a pH of 6 to 7. In all the 

 experiments there was some change in the pH value of the solution 

 containing the fungus. The average pH during the experiment is 

 therefore taken in all cases as the pH of the experiment. 



In the following account the rate of respiration at neutrahty is 

 arbitrarily designated as normal. 



The preliminar}'' work was started with solutions having a pH of 

 about 4. With this hydrogen ion concentration there was no appar- 

 ent effect. Next a solution of pH 2 was tried. Contrary to what 

 was expected this concentration caused a considerable rise in the first 

 half-hour followed by a fall below normal during the second half-hour. 



After the preliminary experiments had given this result more care- 

 ful experiments were made. The first concentration to be used was 

 pH 1.35. This gave a rise of 20 per cent during the first 20 minutes, 

 which was followed by a fairly rapid fall below normal. The second 

 concentration to be used was pH 1.95. The rise in this case was more 

 gradual than in the preceeding one and the fall was also much more 

 gradual and did not fall nearly so much. A few experiments were 

 also made with pH 1.10. These were similar to those with pH 1.35 

 except that the decrease was sharper and greater. Solutions of pH 

 1.70 gave results very much like those with pH 1.95. 



A large number of experiments were made with pH 2.65. These 

 results were rather variable. With only a few exceptions the rate of 

 respiration was always at or above normal during the entire experi- 

 ment. The experiments that gave the most divergent results were 

 rejected, and from the remainder an average curve was constructed, 

 which for 80 minutes did not fall below normal (Figs. 1 and 2). 



