310 



PROTOPLASM 



to "syrup of violets" as a color indicator. He expressed par- 

 ticularly his surprise and admiration on learning that not only did 

 "spirit either of salt or vinegar, or almost any other eminently 

 acid liquor" turn the syrup of violets red but "a Httle oil of 

 tartar per deliquium, or the like quantity of solution of pot-ashes " 

 turned the syrup into a perfect green. More recently, blueberry 

 and red-cabbage juice have been used. Red-cabbage juice gives 

 a good range in color changes from deep red to blue-green. The 

 range is as follows: 



Willstatter noted that anthocyanin is responsible for both the 

 color of the rose and that of the cornflower; the colors are differ- 

 ent, because the former is at a pH of 5.5 while the latter is 7.2. 

 E. Philip Smith found the anthocyanin pigments of a number of 

 flowers to show in test tubes colors comparable to those in the 

 living petals, so that by matching the petal with the pH color 

 standards, the pH of the cell sap can be estimated. The flowers 

 examined showed pH values of 3.1 to 7.7. The red group is 

 acid, and the blue alkaline. The method allows observing pH 

 changes during opening and withering and the effect of environ- 

 mental conditions on flowers. 



There are also yellow pigments in plants which serve as pH 

 indicators both within and without the plant. A number of 

 these have been calibrated, including that from the Plasmodium 

 of the slime mold Physarum polycephalum. This pigment, which 

 is possibly a flavone (page 517), has a color and pH range as 

 follows: 



pH 



<1 

 1.5 

 2 

 3 

 4 



Color 



Deep red-orange 

 Red orange 

 Deep orange 

 Orange 



Yellow-orange 



pH 



5 



6 



7 



8 



>8 



Color 



Yellow 



Lemon yellow 

 Sulphur 

 Yellow-green 

 Green 



