observation and description of penicillia 41 



Details of Structure 

 conidiophores 



Essential data regarding conidiophores include their length, septation, 

 the diameter of their cells, and especially their origin in relation to the 

 substratum and to each other. The walls of the conidiophores may be 

 smooth and thin or may be variously roughened, with aerial portions ap- 

 pearing delicately echinulate, granular, or asperulate. In some cases, 

 such as Penicillium roqueforti, these may be marked by conspicuous con- 

 cretions or warts. Differences in the conidiophore wall run consistently 

 through certain series of species, hence must be carefully observed. In 

 other series this character tends to vary markedly with the culture medium. 

 For example, in certain species of the Fasciculata and Divaricata, conidio- 

 phores may appear smooth upon Czapek but definitely rough upon malt 

 agar. Separations of considerable usefulness, however, can still be based 

 upon this character since species belonging to some series appear to be 

 capable of developing roughness under all, or certain specific conditions; 

 whereas the conidiophores of species belonging to other series remain 

 smooth under all conditions. 



Although extremes of variation in the length of conidiophores are usually 

 marked in any culture, the majority of conidiophores in most cultures will 

 approximate an average length. This length, to be most reliable, must be 

 taken from the origin in another hyphae to the lowest branch of the peni- 

 cillus. ^^alid data on conidiophore lengths in many species can be best 

 obtained by direct observation of the undisturbed colony under the micro- 

 scope instead of by the study of fluid mounts. 



The conidiophore may be simple and unbranched, or variously branched. 

 It may arise from vegetative hyphae within the substratum or from aerial 

 vegetative hyphae variously arranged. It may stand alone, or be more 

 or less closely aggregated into clusters, fascicles, or definite coremia. 



The conidiophore of Penicillium typically lacks the differentiated foot- 

 cell so characteristic of Aspergillus as indicated by Thom and Church in 

 1926 and subsequently by Thom and Raper (1945). While species with 

 difficulty interpretable structures are sometimes found, the distinction 

 remains generally definite and rather easily demonstrable. Exceptions 

 are seen in George Smith's two species, Penicillium varians and P. palli- 

 dum (1933), where structures simulating, if not actually representing, foot- 

 cells are regularly seen. In these cases, however, the patterns of conidial 

 structure so complete aligns these forms with Penicillium as to leave no 

 question regarding their proper assignment in this genus. 



