OBSERVATION AND DESCRIPTION OP PENICILLIA 39 



mutants are kno^vn for P. frequentans, P. notaturn, P. chrysogenum, and 

 P. rugulosiim. In none of these cases do the mutants seem to differ, 

 except in conidial color, from the parent strains as these are maintained 

 in culture, hence they are not regarded as separate taxonomic entities. 

 Thom, in 1930, established P. digitatum var. californicum to identify a 

 white conidial form, obviously representing P. digitatum in morphology 

 and physiology, which was sent to him by Professor Fawcett in California. 

 Recognition of this variety should probably be withdrawn since it does not 

 differ from the typical species more than any of the above color mutants 

 differ from the normal "green" parent cultures from which they were 

 derived. Color mutants similar to the above are regularly encountered 

 among the strains developing from conidia exposed to artificial stimuli 

 such as ultra-violet and X-ray radiation, neutron bombardment, etc. 

 They have been reported by Raper and Fennell (1946), Beadle (corre- 

 spondence), Hanson, ei al. (1945), and others. 



Not all white or tan-spored Penicillia can be regarded as mutants. 

 Penicilliuni caseicolum Bainier, for example, is characterized by colorless 

 conidia, yet has been recognized as a valid species significant in the ripen- 

 ing of soft cheeses of the Camembert type for more than four decades. 

 More recently George Smith (1939) described a species, P. carneo-lutescens, 

 which produces conidia light pink in color but is not lalo^vn to closely 

 approximate any recognized green-spored form. 



DEFICIENCY MUTATIONS 



Mutants characterized by striking nutritional deficiencies are sometimes 

 isolated from nature, and regularly occur in considerable numbers among 

 strains developing from conidia exposed to radiations or other external 

 stimuli. In addition to the above mentioned strain of Penicillium citri- 

 num which is unable to utilize nitrate nitrogen, we have also identified 

 an isolate of P. purpurogenum which is unable to utilize sucrose due to an 

 apparent invertase deficiency. Several additional strains have been ob- 

 served to develop in a manner typical of well-recognized species upon an 

 enriched medium such as steep agar, but to grow sparsely and very atypic- 

 ally upon standard Czapek's agar. In these latter cases nutritional de- 

 ficiencies, unidentified as yet, obviously exist. To a considerable degree 

 P. tardum behaves like a mold suffering from some type of nutritional 

 deficiency (see pp. 651-653). 



Working with Penicillium notatum and P. chrysogenum, Bonner (1946) 

 reported the production of a whole series of mutations characterized by 

 their inability to produce various essential vitamins and amino acids. 

 Mutations of well-recognized species characterized by nutritional de- 

 ficiencies, like those based upon color, are not accorded taxonomic status; 



