40 A MANUAL OF THE ASPERGILLI 



the inoculum from a colony in a petri dish by working under a 10 X pocket 

 magnifier, or under a binocular microscope of the Greenough type carrying 

 similarly magnifying lenses. Material to be removed can be exactly lo- 

 cated in the parent colony. It is found possible in dealing with most 

 Aspergilli (1) to remove conidia from a single head, (2) to remove one or 

 more heads borne upon a single hypha at the margin of the colony, or (3) 

 to select vegetative hyphal tips from a single mycelial sector. It is usually 

 possible to avoid (1) heads and conidia of other species or strains, (2) foreign 

 mycelia, and (3) bacterial contaminations present in the substratum. 

 Purity in repeated culture over many years has been possible by this pro- 

 cedure. 





h 



B 



Fig. 10. Single and three-point cultures of Aspergillus foetidus on Czapek's solu- 

 tion agar, room temperature, 10 days, X i approximately. Note that spore produc- 

 tion extends to the colony margins in the central triangle of 'figure B, and almost to 

 the outer colony margins as well. In figure A, sporulation is limited to the central 

 area only. Figure B is favorable for direct examination with the low power objective 

 of the compound microscope; figure A is not. 



Dilution Cultures 



If dilution cultures are to be used, the suspension of conidia should be 

 sufficiently dilute so that the individual petri dish will show not more than 

 six, but preferably not over three, colonies. Such dilutions are difficult to 

 gauge and often result in some plates crowded with numerous colonies while 

 others contain none. The colony locations are not under control. In 

 general, the dilution of spores in successive water blanks with the subse- 

 quent plating of aliquots from such dilutions has not been found sat- 

 isfactory. 



An alternate technique involves the introduction of one loopful of inocu- 

 lating material into a tube of melted agar which is then rolled or shaken, 



