CULTIVATION AND PRESERVATION OF PENICILLIA 83 



esting to note that during this time these old stocks had been stored for a 

 considerable period in a room where the temperature commonly reached 

 35 to 40°C. during the summer months. In no other series was a com- 

 parable longevity encountered. Scattered ascosporic strains in the P. 

 javanicum, Carpenfelcs, and P. luteum series yielded viable cultures, as 

 did also occasional members of the P. rugulosum and P. purpurogenujn 

 series. In many of the better known series represented by such species as 

 P. roqueforti, P. stoloniferum, and P. nigricans all of the strains were dead. 

 Strains of Paecilomyces, like members of the P. chrysogenum series, repre- 

 sented an exception with the majorit}' of strains remaining viable 

 after five years. In contrast to the long-lived forms, some species of 

 Penicillium, such as P. italicum and P. digitatum , usually lose their via- 

 bility in less than a year unless the}^ are stored at refrigerator temper- 

 atures. 



DEGENERATION 



Our Collection of Penicillia, upon which the current study is largely 

 based, contains strains of a number of species isolated in 1904. Other 

 forms go back from 30 to 40 years in continuous culture. Some strictly 

 conidial strains, such as Penicillium roqueforti (NRRL 849) and P. camem- 

 berti (NRRL 877) have remained unchanged when transferred with rigor- 

 ous care. Other conidial forms handled with equal care have shown pro- 

 gressive variation and degeneration in culture. Thom's type of P. 

 oxalicum (NRRL 787), which originally represented a strictly velvet}^ and 

 heavily sporing strain, now produces rather floccose and lightly sporulat- 

 ing colonies quite unlike the original. Penicillium purpurogenum var. 

 rubri-sclerotium, when first isolated, produced sclerotia and abundant 

 typical biverticillately sjonmetrical penicilli in culture. Sclerotium pro- 

 duction has been lost completely and today this strain produces colonies 

 atypical in pattern and texture which sporulate lightly upon all substrata 

 In both of these strains, however, cellular elements of the penicilli remain 

 characteristic of the species and there can be no question of continuity 

 in culture from the original strain. 



Loss of ascospore production represents a common occurrence in strains 

 characterized by abvmdant perithecia and ascospores when first isolated. 

 This has sometimes been attributed to the gradual elimination from such 

 a culture of one of the haplonts necessary for development of the perfect 

 stage. Emmons (1935), however, showed that all of the species of Peni- 

 cillium studied by him were homothallic and capable of developing colon- 

 ies with typical perithecia when started from either individual conidia or 

 ascospores. Loss of the ascosporic stage must, therefore, be sought in 

 some other source, possibly nutritional in character. 



