158 



THE ASCOMYCETES 



Although cleistothecial formation is not known to occur gen- 

 erallv among species of Penicillium, it is of rather common oc- 

 currence in certain ones, notably P. avellaneinn, P. spiciilisponmi, 

 P. liiteiim, P. glaiiciim, P. brejeldianimi, and P. javaniciim. 



Fig. 54. Development of Penicillium. A, B, and C. Conidiophores and 



conidia of P. roqueforti. D, E, F, and G. P. criistacenm. (Adapted from 



Brefeld.) D. Coiled antheridial and ascogonial hyphae. E. Ascospores. F. 



Cleistothecium in surface view. G. Clusters of asci. 



Classification. The treatises by Thorn (1910, 1930) bring 

 tos^ether for the svstematist means for identification of this diffi- 

 cult group of species. He treats Penicillium as a form genus, for 

 the reason that so few species are known to possess a perfect 

 stage. The nature of the colonies (whether, for example, they 

 are velvety, compact, or arachnoid), the type of branching of 

 conidiophores, the production of sclerotia, the degree of spread- 

 ing or compactness of the penicillus, and the color of conidia 



