392 A MANUAL OF THE PENICILLIA 



of Calif.) and Miller, et al. (U.S.D.A.) discovered independently that ethyl- 

 ene was evolved by citrus fruits, and that decaying fruits produced more 

 than sound ones. It was further shown in both investigations that Peni- 

 cillium digitatum is capable of producing ethylene, thus further hastening 

 the coloring process. 



Penidllium digitatum grows very poorly upon Czapek's solution agar 

 and other "synthetic" media, but grows luxuriantly upon "natural" sub- 

 strata such as malt and potato-dextrose agars. In our experience, P. digi- 

 tatum has often been observed to grow luxuriantly upon Czapek agar in 

 plates contaminated with other mold fungi. An explanation of this be- 

 havior is found in the work of Wooster and Cheldelin (1945). Studying 

 the nutrition of P. digitatum under carefully controlled conditions, these 

 investigators found that thiamin, or the thiazole moiety, was required, and 

 that a quantitative increase in growth could be obtained over a range from 

 0.01 to 3.O7/25 ml. of culture solution. Other vitamins, including pyri- 

 doxine, pantothenate, and biotin were stimulatory. Glucose afforded a 

 more favorable carbon source than sucrose (which is commonly used in 

 Czapek's agar), and organic nitrogen sources such as asparagine or hy- 

 drolyzed casein were better than NaNOs and other inorganic salts. Elze 

 (1934) reported P. digitatum. to grow more luxuriantly and to be more 

 virulent in the presence of Diplodia natalensis than when inoculated into 

 oranges singly A synergistic effect was observed between P. digitatum 

 and Oospora citri-aurantii in laboratory cultures by Gemmell (1939), who 

 demonstrated also that these fungi produced more rapid and extensive 

 rotting of fruit when inoculated together than when either one or the other 

 was present as the sole pathogen. 



Birkinshaw, Charles, and Raistrick (1931) have reported limited bio- 

 chemical studies on Penidllium digitatum. Considerable ethyl acetate was 

 produced from glucose, and in addition some ethyl alcohol and a new poly- 

 saccharide which gave rise to glucose upon hydrolysis. 



Penicillium roqueforti Series 

 (Roquefort-type Cheese Molds) 

 Outstanding Characters 



Colonies usually but not always broadly spreading, velvety, azonate, gener- 

 ally thin, with abundant short conidiophores arising from trailing hyphae 

 or submerged hyphae just below the agar surface, growing margin com- 

 monly appearing arachnoid or cobwebby, conidial areas typically in 

 dark yellow-green shades, often showing greenish to almost black shades 

 in colony reverse. 



