78 A MANUAL OF THE PENICILLIA 



In Scopidariopsis, a genus of molds often regarded as closely related to 

 Penicillium, an entirely different response is often noted. In many 

 strains, growth is poor or negligible upon malt agar that is strongly acid 

 in reaction but fairly luxuriant upon substrata approximately neutral in 

 reaction. The same response is seen in Penicillium albicans, a species 

 suspected of being closelj^ related to Scopulariopsis. 



HUMIDITY 



In cultivating the majority of Penicillia on agars of the usual nutrient 

 concentration and firmness, no special precaution regarding humidity 

 need be taken except that tube cultures should be stoppered with fairly 

 compact cotton plugs, and that petri dishes should be fairly close fitting. 

 When testing strains of Penicillium expansum or P. italicum and P. digi- 

 tatuni for their capacity to rot pomaceous or citrus fruit respectively, it is 

 advisable to incubate the inoculated fruit in desiccators or other vessels 

 where a humid atmosphere can be maintained if one wishes to secure the 

 maximum and most characteristic development of these fimgi on the sur- 

 face of the rotting fruit. 



Preservation of Cultures 



Any method of cultiu'e preservation, to be successful, should preserve 

 cultural, morphological, and physiological or biochemical characteristics 

 in as nearly unaltered form as possible. For spacific strains, methods 

 may need to be altered to accomplish this objective. Particular attention 

 shDuld be given to the perpetuation of cultures which represent species 

 types, and strains which are significant for their biochen.i3al reactions. 

 There should be no question regarding the continuity in culture of par- 

 ticular strains which for one reason or another it is important to maintain. 

 The careful worker may be able to determine whether or not he is working 

 with an organism culturally and morphologically similar to one previously 

 reported; he cannot, however, without actual test, loiow whether he is 

 dealing with a strain responsible for a desired biochemical reaction. Vari- 

 ous methods of culture preservation have been successfully applied to the 

 Penicillia and other molds in our Laboratory over a period of years, and 

 were given rather detailed consideration in Thom and Paper's "Manual 

 of the Aspergilli" (1945). Hence, it should be sufficient to review these 

 only briefly in the present work. 



TYPES OF cultures 



Agar Slants: The method generally employed for maintaining mold 

 cultures, and one which has been successfully used in our laboratories over 

 a period of more than four decades, may be referred to as the "agar slant 



