110 A MANUAL OF THE PENICILLIA 



dustry, or which show unique biochemical activities, have not been found 

 to produce perithecia or ascospores in spite of diligent search and experi- 

 mentation. The student or investigator concerned with the distribution 

 and activities of the Penicillia must, therefore, find some basis other than 

 the development of an ascosporic stage for the separation and identification 

 of his species. 



An obvious alternate choice is to use the asexual conidium-producing 

 structures, or penicilli. This is precisely the course that has been followed 

 by all investigators since Link established the genus Penicillium in 1809. 

 Brefeld (1874), Zukal (1890), Wehmer (1893), Klocker (1903), Dangeard 

 (1907), Thom and Turesson (1915), Lehman (1920), and others have de- 

 scribed ascosporic species and added these to Link's genus without seriously 

 considering the separation of such forms from the vastly greater number of 

 asexual species. The genus Penicillium is regarded as properly assigned 

 among the Ascomj^cetes despite the fact that most species fail to show an 

 ascosporic phase, and despite the additional fact that in the taxonomy of 

 the genus conidial structures are general^ regarded as outweighing peri- 

 thecia in indicating broad relationships. 



Systems of classification proposed by earlier investigators have proved 

 inadequate, hence have undergone frequent change or amendment. The 

 system proposed by Thom in 1930 may in time also prove inadequate. 

 However, it has been generally adopted in this country and abroad, and 

 has fui-nished a working basis for the identifications necessary to intelligent 

 discussion and reporting of species of Penicillia in relation to practical 

 problems and applications. With minor emendations to include additional 

 species described since 1930, and with certain changes dictated by the 

 continued comparative study of species already Imown, Thorn's bases of 

 separation within the genus as proposed in his Monograph (1930) are fol- 

 lowed in the present J\Lanual. 



The primary basis of separation within the genus Penicillium rests upon the 

 pattern and complexity of fhe conidial structure, or penicillus. Upon this 

 criterion four (4) major sections are established as follows: 



Monoverticillata: Conidial structures typically consist of a single verticil 

 of sterigmata, or conidium-bearing cells, terminating a fruiting branch, 

 or conidiophore (fig. 8). The conidiophores may arise directly from 

 mycelia contained in the substratum, or as lateral branches from aerial 

 hj^phae, variously interwoven or less commonly arranged in more or less 

 well-defined ropes. In certain forms the conidiophores are irregularly 

 branched but the individual fruiting structure still retains its basic mono- 

 verticillate character. Wehmer, followed by Sopp, Bainier, and others, 

 referred monoverticillate species to the genus Citromyces. Thom (1930) 



