82 



A MANUAL OF THE PENICILLIA 



sterile mineral oil, usually extending about 1 cm. above the edge of the 

 agar slant or colony margin. Exact figures on viabilities are not avail- 

 able, but reports have been received covering three to four years. The 

 method is considered to be especially adaptable to the preservation of 

 forms that sporulate very lightly since mycelial elements, as well as propo- 

 gative cells such as conidia appear to retain their viability. Buell and 

 Weston (1947) discussed this technique and presented favorable results 

 obtained over a two-3^ear period. 



Fig. 22. Storage of l_yop/iilized cultures, showing tiie limited space required. A 

 metal box 12^ inches by 14f inches will accommodate 306 vials, each containing four 

 desiccated preparations as shown. 



LONGEVITY 



Species of Penicillium vary materially in their ability to remain viable 

 in laboratory cultures. Some series survive for several years when stored 

 as dry agar slants; others die off fairly rapidly. Some series of transfers 

 have been made to reach a basis for generalization but the factors involved 

 are too numerous to justify generalization. In oiu- experience, members 

 of the Penicillium chrysogenum series have been found to be especially 

 long-lived. Of a total of 42 strains belonging to this series, which were 

 brought to the Northern Laboratory in 1940, all but three were found 

 to be viable in agar slant tubes when tested five years later. It is inter- 



