PREFACE 



Mycologically, Penicillium as the generic name of a group of green molds 

 has been kno\\Ti for one hundred and forty years. Studies .in this 

 group were mainly floristic up to 1890. Green molds were everywhere 

 and names for them appeared in every enumeration of the fungi of a par- 

 ticular locality, or of the species encountered in the study of decomposing 

 or fermenting substances. Saccardo (1880) followed by Wehmer (1894, 

 1895) reported Penicillia active in the destruction of citrus fruit. Wehmer 

 (1893) reported certain of them to be active producers of citric acid. 

 Johan-Olsen (Sopp) (1898) related them to the cheese industry. The 

 development of culture laboratories during this period made possible their 

 isolation and examination in pure culture; and subsequent physiological 

 studies led to increasing interest in their presence and significance. 



Nevertheless, intensive study of the Penicillia was limited to less than a 

 dozen laboratories, including those of Welimer, Bainier, Sopp, Thom, 

 Westling, Biourge, Zaleski, Van Beyma, and Raistrick, until the antibiotic 

 penicillin was brought to America in 1941. Thenceforward, instead of 

 individuals or small groups, hundreds of workers including bacteriologists, 

 pharmacologists, chemists, and chemical engineers, turned their attention 

 to the Penicillia. Instead of a casual academic pursuit, the identification 

 of these organisms became a matter of prime biochemical and industrial 

 importance. A restudy of the genus seemed urgent. 



Thom's Monograph, The Penicillia, was published in 1930. In the 

 intervening years, various new surveys have been made, many new species 

 have been described, and biochemical investigations have directed special 

 attention to many selected species. Finally the development of penicillin 

 shifted the emphasis from single strains, often discussed as species, to the 

 recognition of groups of variants bridging many of the gaps separating 

 strains formerly given varietal or specific rank, ]\Iean while, the accumula- 

 tion of large numbers of strains, representing all of the major groups, made 

 available sufficient material to support a systematic restudy of all of the 

 Penicillia. 



Upon the establishment of the Northern Regional Research Laboratory 

 of the Bureau of Agricultural and Industrial Chemistry, U. S. Department 

 of Agriculture, at Peoria, Illinois, the development of a collection of pure 

 cultures of micro-organisms significant to agriculture and industry was 

 undertaken. Raper, who had worked with Thom for the preceding decade, 

 was transferred from the Laboratory in Washington to take charge, and 

 brought with him cultures of all molds from the Thom Collection. Upon 

 the retirement of Thom in 1942, all records and descriptive material ac- 



vii 



