CORRELATION OF REACTION OF THE SOIL 159 



These determinations of pH may not necessarily be those of 

 the vacuolar sap, just as the pH of the crushed tissues of green 

 plants may not be that of the cell sap. They appear of interest 

 in indicating that fungus tissues are acid. Recognition of their 

 significance, however, awaits the development of methods for 

 determining true pH values of fungus-cell sap. 



pH and pigmentation. The pigments in many species of 

 fungi may function as natural indicators that change color with 

 a change of reaction. One factor that controls the" development 

 of pigment, moreover, is the reaction of the medium. The pres- 

 ence of appropriate carbohydrates may also constitute a control- 

 ling factor. These relationships with species of Fusarium were 

 studied by Sideris (1925). If he employed dextrose solutions and 

 made no attempt to control the changes in reaction during growth, 

 pigment was produced within the range pH 3.0 to 7.5. If the pH 

 was kept constant, pigment was produced only within the rano-e 

 3.5 to 5.5. 



pH and enzymic activity. The effect of pH on enzymic ac- 

 tivity was mentioned in Chapter 2. Evidently the effect of re- 

 action upon individual metabolic processes in fungi has not been 

 the subject of much study. Karrer ( 192 1 ) recorded that Fusarium 

 sp. from cotton, when grown in nutrient solution, yield the great- 

 est total amount of amylase if the initial reaction is pH 4.5 and the 

 final reaction is pH 7.8; Collet otrichum gossypii, if the initial re- 

 action is pH 7.0 and the final is pH 7.9. For Fenicilliinn italicum 

 pH 3.0 and pH 4.5 are equally favorable. Amylase accumulation 

 is completely inhibited within the range pH 9.0 to 1 1.0 in Fusarium 

 sp. and in C. gossypii, and at pH 9.0 in P. italicum. Further evi- 

 dence of the influence of hydrogen-ion concentration upon the 

 activity of amylase was presented by Sherman, Thomas, and Bald- 

 win (1919). They showed that pancreatic amylase is active within 

 the range pH 4.6 to 10, pH 7.0 being optimum; malt amylase 

 within the range pH 2.5 to 9.0, pH 4.4 to 4.5 being optimum'; and 

 amylase from Aspergillus oryzae within the range pH 2.6 to 8.0, 

 pH 4.8 being optimum. 



Correlation of reaction of the soil, optimum pH of the 

 pathogen, and incidence of disease. Experimentation involving 

 these matters in connection with soil-borne pathogens has en- 

 gaged the attention of certain plant pathologists, notably Chupp 



