582 INTRACELLULAR ACIDITY IN VALONIA 



tion of alkalinity, conditioned by photosynthesis, and by the pulsatile 

 supply of "outside" water to the creek at periods of high-tide, was 

 regularly observed. Over the reefs a less extensive daily rhythm of 

 variation in alkalinity was noted (cf. McClendon, 1918), the reac- 

 tion of the ocean water being at pH = 8.1 to 8.2; the variation here 

 concerned depended, in part, upon the ebbing of water from semi- 

 enclosed sounds. 



The acidity of the sap of Valonia under these differing external 

 conditions was found, however, to be sensibly the same in all cases, 

 even when the temperature varied from 18-28°C., at different times 

 of the year. 



No effect of darkness {i.e. cessation of photosynthesis) could be 

 detected in the sap reaction, either in the field or when the cells were 

 kept in darkened aquaria for some hours. 



For the field measurements in particular, it was necessary to use 

 various indicators in connection with buffer solutions. The sap 

 to be tested was secured by first rinsing a selected cell rapidly in 

 distilled water, drying it with filter paper or a soft cloth, then punc- 

 turing the cell-wall with a glass needle, thus allowing the sap to 

 flow out into a test-tube. The addition of 1 to 2 cc. of sea water to 

 10 cc. of sap is sufficient to change the pH from 5.9 to 7.0, — hence 

 contamination with sea water had to be avoided. Carbon dioxide, 

 moreover, is readily lost by the Valonia sap, in which it exists at a 

 considerable tension, so that squirting the sap through the air from 

 a small puncture in the cell was not permissible. 



In aquaria, Valonia quickly increases the alkalinity, through 

 photosynthetic abstraction of CO2, and can in this way bring about 

 an external alkalinity of pH = 9.5, or even greater (cf. Moore and 

 others, 1914; Crozier, 1919). But the internal acidity seems to be 

 constantly maintained, even under these extreme conditions, at a 

 little less than pH = 6.0. The same was found in moderately hypo- 

 alkaline sea water (pH = 7.8 to 7.9). This finding indicates that 

 in a method of studying photosynthesis, for example, such as that 

 devised by Osterhout and Haas (1918), the varying external reac- 

 tion forming the basis of the measurements does not itself materially 

 affect the internal acidity, the latter presumably being the immediate 

 regulator of respiratory and other protoplasmic processes. 



