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A MANUAL OF THE ASPERGILLI 



sporing colonies; forms producing restricted colonies characterized by the 

 production of an excessive amount of orange-brown exudate; and forms 

 with leathery, close-textured colonies bearing very few conidial heads 

 (PI. II, D). Alterations in microscopic details commonly accompanied 

 these changes in colony appearance (fig. 19). In addition to these morpho- 

 logical mutants, which were found to be stable when checked through ten 

 successive transfers over a period of 12 months, various physiological 

 mutants were also isolated. These included forms unable to utilize nitrate 

 nitrogen (PI. II, E) but able to grow and sporulate normally upon media 

 containing ammonia nitrogen, and a form unable to synthesize thiamin 

 (PI. II, F). Upon Czapek's solution agar containing sodium nitrate and 

 sucrose, each of these is strikingly different from the parent strain; upon 



A 



Fig. 18. Induced mutation. A and B, Aspergillus niger group, strain NRRL No. 

 67: A, parent culture growing on Czapek's solution agar, 10 clays, room temperature; 

 B, tan-spored mutation of same produced by ultraviolet radiation. 



malt extract agar, which contains adequate amino nitrogen and thiamin, 

 neither could be differentiated from the parent (Raper, Coghill, and Hol- 

 laender, in press). Thus the need for comparative study and examination 

 upon a variety of media is apparent, while the importance of such studies 

 in reliable taxonomic work cannot be over-emphasized. In cultures of 

 Aspergillus terreus resulting from irradiated spores the capacity to produce 

 itaconic acid varied from zero in some isolations to levels somewhat above 

 the parent culture in others. The majority of such isolations produced 

 yields somewhat lower than the parent strain, many produced yields ap- 

 proximately equal to it, while a very few produced superior yields (Lock- 

 wood, Raper, Moyer, and Coghill, in press). 



Based upon our own investigations and the published reports of other 



