330 PROTOPLASM 



animals. Eggs of echinoderms (sea urchin), a tunicate, and a 

 worm are all about pH 6.6; yeast and other fungi (Fusarium) 

 are between 5.9 and 6.1. 



The protoplasm of the cells of higher plants appears to have a 

 fairly constant pH value, being in this respect comparable to 

 animal protoplasm (though there is some difference of opinion). 

 The value generally accepted is 6.8 to 7.0. The pH of slime 

 mold (Physarum) protoplasm, as indicated by its own natural 

 indicator, a yellow pigment, is 6.2. 



Extremes on the acid side of protoplasm may be great but not 

 in view of the extraordinary behavior of certain plants. Some 

 fungi (Penicillium) can grow on strong solutions of acid or 

 on the underside of corks of bottles of acid. Extremes omitted, 

 protoplasm is usually just on the acid side of neutrality — about 

 pH 6.8. But Spek finds that there is not one pH value for 

 protoplasm; in Amoeba, the thinner, fluid portion which advances 

 at the tip of a pseudopodium has an acidity value of pH 7.3, 

 while the inner (granular) protoplasm is 5.2. 



Acidity determinations of plant sap, in particular the sap that 

 fills the vacuoles of plant cells, are more readily made and are 

 likely to be more accurate than those made of the cytoplasm. 

 Dyes may be directly injected into the cell vacuole, the color 

 change observed, and the pH value noted; or the cells may be 

 bathed in dyes that penetrate easily. Often, the vacuoles 

 contain pigments that are pH indicators. The colors of flowers, 

 leaves, and fruits are due to pigments usually dissolved in the 

 cell sap, i.e., in the vacuole; less often is the pigment directly 

 in the cytoplasm. Acidity values of plant sap range from 

 pH 1.4 (G. N. Watson found this value for the India berry) to as 

 high as pH 10. Values of the pH of cell sap are significant in 

 themselves, but it is erroneous to regard a pH determination of 

 the sap as indicating the acidity of the cytoplasm; the two may 

 be of the same value, and undoubtedly the one influences the 

 others, but the sap may be highly acid, and the cytoplasm near 

 neutrality. 



Attempts to measure the pH of the cell nucleus with dyes have 

 been made, but the results are questionable, as a stained nucleus 

 is usually a dead one. Results indicate a pH of 7.5 or 7.6 for 

 the nucleus, as compared with 6.8 for the cytoplasm. The solu- 

 tion in which cells are bathed (blood plasma and tissue juices) 



