CULTIVATION AND EXAMINATION 45 



Hanging Drop Cultures 



The drop of culture fluid inoculated with conidia and hanging from a slide 

 or cover glass into a closed chamber can be incubated and examined readily. 

 It furnishes information as to the percentage of conidia which are viable, 

 the changes which occur in the germinating spore, such as swelling, bursting 

 along definite lines, germination from specialized germ-pores, or branching 

 of the germ tube, but descriptions of fruiting structures in such hanging 

 drops are worthless in the study of the mold colony or normal fruiting habits 

 of the species. 



TEMPERATURE 



The great majority of Aspergilli grow well and sporulate abundantly at 

 temperatures of 23° to 26° C. For this reason, most cultures can be incu- 

 bated on laboratory tables or shelves, and it is not necessary to give special 

 consideration to incubation. There are, however, certain exceptions. 

 The large-spored members of the Aspergillus glaucus group, such as A . echin- 

 ulatus and A . niveo-glaucus, grow more rapidly and fruit more abundantly 

 at 20° than at 24° to 25° C. (Thorn and Raper, 1941). This temperature 

 response is especially marked in A. medius: at 18° to 20° C. growth is rapid, 

 abundant large conidial heads are produced, and numerous perithecia are 

 developed ; at 25° C. and above, growth is restricted, few and smaller conidial 

 heads are developed, and only occasionally perithecia are produced (fig. 12). 

 On the other hand, the very abundant small-spored members of the A. 

 glaucus group, such as A. re-pens, A. chevalieri, and A. amstelodami, grow 

 rapidly and fruit abundantly at 30° C. (Thorn and Raper, 1941). In A. 

 janus (Raper and Thorn, 1944), two different types of conidial heads are 

 produced and the ratio of these types is strongly influenced by temperature 

 (fig. 12): at 18° to 20° C. almost all heads are white with clavate vesicles 

 and are borne upon long conidiophores ; at 30° C. almost all heads are dark 

 green with globose vesicles and are borne upon short conidiophores (see 

 species description, p. 187). 



When grown upon suitable media and incubated at 20° C. in the presence 

 of light or alternate light and darkness, Aspergillus giganteus produces 

 large heads on long conidiophores ranging up to 5 or even 10 cm. In similar 

 cultures incubated at 30° C. heads are smaller and conidiophores are uni- 

 formly short, rarely exceeding 1 cm. in length, whether the cultures are ex- 

 posed to light or incubated in total darkness. A. terreus, A. carneus, and 

 A. fischeri thrive at temperatures up to 35° C, while A. fumigatus grows 

 well at 45° or even 50° C. In all of these forms growth is more rapid and 

 sporulation more abundant at 30° C. than at normal laboratory tempera- 



