CULTIVATION AND PRESERVATION OF PENICILLIA 65 



and reproducible medium gains a decided advantage to the describer so 

 long as the growth obtained has well-marked characters and maintains 

 the vigor of the strain of mold studied. In his Monograph, Thom (1930) 

 based descriptive data almost exclusively upon this medium. In the 

 present study species diagnoses are centered upon the same substratum, 

 with supplemental data supplied from other media, particularly malt ex- 

 tract agar and a steep liquor enriched Czapek's solution referred to as 

 "steep agar." The markedly different growth response exhibited by cer- 

 tain species and strains when cultivated upon these different substrata is 

 strikingly sho^vn in figure 17. 



In maldng Czapek's solution agar the neutral potassium phosphate is 

 preferred to the acid form of the salt, since with the neutral salt the final 

 reaction of the medium is neutral or only very slightly acid, showing a 

 reaction of pH 6.8 to 6.9. Opinions differ, and many workers prefer the 

 medium of lower pH resulting from the use of the acid salt. Czapek's 

 solution agar is not offered as an optimum substratum for any particular 

 species, but as a mixture approximately neutral in reaction, which is read- 

 ily made in any laboratory in fairly uniform manner, and which permits 

 moderately vigorous growth of nearly all saprophytic Penicillia. The 

 quantities of mycelium and conidia produced b}^ many forms in other 

 media are much greater; but for comparative study in the majority of the 

 species a moderate growth is generally more useful than the great masses 

 of mycelium and conidia which are readily obtained by using richer sub- 

 strata. 



Substitution of glucose for sucrose provides a medium which is more 

 favorable for certaia strains and species. 



Czapek solution agar containing 20 percent, rather than the usual 3 

 percent sucrose, is routinely used for cultivating members of the Asper- 

 gillus glaucus group (see Thom and Raper, 1941). The same high sugar 

 medium is occasionally very useful for secvu'ing conidial structures in 

 certain species and strains of Penicillium which sporulate very lightly or 

 not at all on standard Czapek agar. In a few cases, e.g., Penicillium levi- 

 tum Raper and Fennell, descriptive notes from this medium are incorpor- 

 ated into the species diagnosis. 



In their earlier studies on the biochemistry of micro-organisms, including 

 many different species of Penicillium, Raistrick and co-workers generally 

 employed a modified Czapek-Dox solution in which 5 percent glucose 

 was substituted for 3 percent sucrose and the NaNOs was reduced from 

 0.3 percent to 0.2 percent. More recently, beginning in 1932, they have 

 commonly employed a modified Raulin's solution referred to as "Raulin- 

 Thom medium" in which glucose is substituted for sucrose and potassium 

 silicate is omitted (see Clutterbuck, et at. Biochem. Jour. ^6: 1444. 1932). 



