Plate II 



-Mutations in Aspergillus terreus Thorn produced by irradiating conidia with ultraviolet light. Colonies 

 tin >\\ n upon C'zapek's solution agar at room temperature for two weeks. A (upper left), Aspergillus terreus, 

 XRRL No. 265, unirradiated stock culture. B (upper right ), Albino mutant, producing white conidial heads 

 but retaining the basic cultural and morphological characteristics of the parent culture. C (center left), floc- 

 cose, yellow-white mutant producing few and atypical conidial heads. D (center right), Leathery mutant, 

 producing tough, close-textured colonies and very few and atypical conidial heads. E (lower left), Nitrate 

 mutant, a form unable to use nitrate nitrogen, producing thin spreading colonies and few but entirely typical 

 heads. F (lower right), Thiamin mutant, a form unable to produce thiamin, producing thin, spreading 

 colonies and very few and atypical conidial heads, see text p. 75. (Color photographs by Haines, Northern 

 Regional Research Laboratory. Reproduced through co-operation of Chas. Pfizer & Co., Inc.) 



