IMPLICATIONS 163 



Attempts to prevent the decay of apples and oranges by use of 

 alkaline dips have been less successful. Marloth (1931) recorded 

 that sodium tetraborate is more toxic to Penicillium dlgitatwn 

 than to P. italicum, but that sodium bicarbonate is more toxic to 

 P. it ah cam. Attempts to prevent decay of citrus fruits by these 

 molds and by Pbomopsis citri and Diplodia natalensis have not 

 been uniformly successful, presumably because the mycelia early 

 become internal to the "buttons" or cut pedicels and because the 

 spores of Penicillium are difficult to wet. 



Implications. The totality of evidence from studies of the ef- 

 fects of reaction on fungi shows convincingly that pH is an en- 

 vironmental factor of enormous consequence in modifying; their 

 metabolic activities. There is specificity of minimal, optimal, and 

 maximal pH requirements, but it must not be overlooked that the 

 effects of the concentration of hydrogen ions cannot be isolated 

 completely from those induced by other ions. These effects are 

 always intricately correlated. For this reason it is not unlikely 

 that in the past too much consideration has been given to the 

 influence of the hydrogen ion and too little to that of other ions. 

 No doubt this situation prompted the supercilious suggestion 

 that doctoral dissertations dealing with these problems may be 

 regarded as fulfilling requirements for the "pH D." 



So long as growth continues in a fungus culture, the reaction 

 of the medium continues to change, although the changes may be 

 masked by relatively large amounts of buffer substances present 

 in the medium. In other words, the analytic and synthetic proc- 

 esses that occur during utilization of organic substrates result in 

 the production of many kinds of organic acids and such other 

 products as pigments, polysaccharides, sterols, and vitamins (see 

 Chapter 4). Among the acids known to be producted by fungi 

 are aconitic, carlic, carlosic, carolic, dimethylpyruvic, fulvic, fu- 

 maric, gallic, glycolic, glycuronic, itaconic, kojic, malic, cf-man- 

 nonic, mycophenolic, oxalic, penicillic, puberulic, pyruvic, spiculi- 

 sporic, succinic, and terrestric. It would seem that determination 

 of the kinds of acids produced in fungus metabolism and the con- 

 ditions influencing their production should be given increasing 

 consideration, rather than devoting so much attention to accumu- 

 lation of data on pH changes during growth. 



