52 A MANUAL OP THE PENICILLIA 



obtained by averaging the dimensions of a large number of cells. In the 

 study of the Penicillia the occasional presence of a greatly enlarged coni- 

 dium, among hundreds that are reasonably uniform in size, scarcely war- 

 rants increasing the range of measurements reported for conidia of the 

 usual diameter. Such observations do suggest, however, a need for fur- 

 ther study to account for the contrast in size. In some cases such enlarged 

 cells may represent conidia in early stages of germination. In other cases 

 they undoubtedly result from an interruption of normal septation at the 

 tip of the sterigma in such a way that the material normally going into two 

 or more conidia becomes contained within a single cell wall. 



Germination of Conidia 



When inoculated into a favorable nutrient, conidia tend to germi- 

 nate in a manner essentially characteristic of the species under examin- 

 ation. In some species conidia swell greatly before putting out one or 

 more germ tubes; some merely "round-up". Furthermore, the number 

 and arrangement of germ tubes may be fairly characteristic in some species 

 and not at all characteristic in others. In the genus Scopiilariopsis, of- 

 tentimes regarded as related to Penicillium, a single germ tube arises 

 only from a special area or germinal pore at the base of the conidium. 

 In Penicillium germ tubes generally seem to be able to arise at almost 

 any point on the cell surface. 



SCLEROTIA 



Sclerotia are characteristic of certain series and species of Penicillium 

 (fig. 13). However, no particular taxonomic significance comparable to 

 that observed in the genus Aspergillus can be attributed to their presence. 

 The latter genus can be separated into two main parts upon the criterion 

 of whether or not sclerotia are produced. In the genus Penicillium, 

 series producing sclerotia are observed in each of the three major sections. 

 Among the Monoverticillata the production of elliptical to globose sclerotia 

 is regularly characteristic of members of the Penicillium thomii series. 

 Typically these consist of very hard masses of pseudoparenchymatous 

 tissue in which the walls of individual cells are veiy thick. Similar sclero- 

 tia are seen in P. raistrickii in the Divaricata, and a considerable degree of 

 relationship to the P. thomii series is suggested. In P. turbatum, of the 

 P. thomii series, and in P. soppi, of the P. raistrickii series, small, soft 

 masses of thick-w^alled cells usually develop (fig. 75). These hardly repre- 

 sent true sclerotia in the sense of P. thomii and P. raistrickii, but their 

 presence is accepted as evidence of relationship to these species, hence 

 their assignment with them. 



Rounded, firm sclerotia are also produced in Penicillium gladioli (fig. 



