CULTIVATION AND PRESERVATION OF PENICILLIA 



77 



temperatures of 37-40°C., as do also species of Scopulariopsis which are 

 often reported as parasitic to animals including man. 



Our experiences indicate that the temperature of incubation should be a 

 part of the record in every cultural description. In the present Alanual 

 this practice has been followed, the temperature being recorded either as 

 24°C., or as "room temperature," which in our air-conditioned Labora- 

 tory generally ranges from 23° to 25°C. 



ACIDITY 



]\Iost species of PenicilUum grow best in a mildlj' acid substratum. 

 Usually, such a favorable reaction is established bj' the mold itself as it 



Fig. 19. Influence of incubation temperature. PenicilUum duponti Griffon and 

 Maublanc emend. Emerson, NRRL 2155, a thermophilic species. A and B, similarly 

 inoculated plates incubated at 25° and 45°, respectively. Steep agar, 10 days. Note 

 complete absence of growth in A and luxuriant growth in B. 



decomposes whatever sugar or carbohj^drate is supplied in the substratum. 

 When Czapek's solution agar containing sucrose is employed, the usual 

 course of development is as follows: The substratum is initially near 

 neutrality or slightly acid, and with the ensuing growth of the mold shifts 

 quickly to acid as the sugar is used up, then returns to neutral or becomes 

 alkaline as relatively greater amounts of nitrogenous materials are broken 

 down, often including the proteinaceous substance of the mold itself. 



In certain species the response to acidity is very striking. PenicilUum 

 digitatum Sacc. grows very sparsely and restrictedly upon the standard 

 Czapek solution agar (fig. 103C), but if the reaction is lowered to pH 4.0 

 fairly luxuriant growth is obtained. To a lesser degree, the same phe- 

 nomenon is observable in P. italicum Wehmer. Both species represent 

 active rots of citrus fruit, hence we can assume that their behavior in 

 culture results from long conditioning and adaptation to their natural 

 habitats. 



