94 



A MANUAL OF THE ASPERGILLI 



strains from various parts of the United States, together with isolations 

 from China, British Guiana, Cuba, Panama and European sources. 



The species description as presented is based upon a large number of 

 closely related strains that have been examined, and is adequately repre- 

 sented by such specific strains as NRRL Nos. 2, 5, 8, and others. 



Upon malt extract agar, details of morphology and colony characteristics 

 may or may not conform with those listed above. For example, in such 

 typical strains as Nos. 2, 5, and 8, conidial structures are generally more 

 abundant upon malt than Czapek's agar and may average as much as 20 to 

 25 percent larger in size. In other strains such as Nos. 4 and 6, a markedly 

 different response is noted upon this medium. Conidial heads, although 



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Fig. 22. Aspergillus clavatus Desm. (Strain NRRL No. 1: Thorn No. 107). A, 

 Colony growing upon Czapek's solution agar, 10 days, room temperature, X 1.3. 

 B, Conidial heads diminutive and somewhat atypical but showing characteristic 

 clavate form, X 600. 



greatly increased in number, are much reduced in size, with conidiophores 

 generally 1 mm. or less in length bearing heads only 100 to 125/x long and 

 proportionately reduced in diameter. In these latter forms, conidia are 

 somewhat irregular in form and generally larger than in the more typical 

 strains first considered. 



Culture NRRL No. 1 (Thorn No. 107) differs markedly from the species 

 description in producing deeply floccose colonies (Fig. 22 A) and compara- 

 tively few spore heads which are extremely variable in size. These range 

 from very small fruiting structures (Fig. 22 B) borne as branches upon 

 aerial hyphae to structures arising from the substratum which are charac- 

 terized by dimensions almost typical of the species. This culture is more 

 nearly normal upon malt than upon Czapek's solution agar but is unique 



