14 CULTURAL STUDIES OF SPECIES OF PENICILLIUM. 



4. Full drawings or photographs should show hahit as well as micro- 

 scopic details of cells and cell relations. 



5. Other morphological or physiological data obtainable should 

 be given as accessory information. Very striking characters are 

 often found under accidental or unique conditions which immedi- 

 ately differentiate particular species. Some of these characters come 

 up in the ordinary course of cultural study, others are found under 

 accidental conditions but could rarely occur in laboratory routine. 



It is clear that such descriptions can only result from repeated cul- 

 ture of a species under constant observation. If the range of such 

 culture has been wide, it will bring out the most striking characters 

 and thus reduce the number of minute distinctions necessary. 



NECESSITY FOR DESCRIBING CULTURE MEDIA AND TEMPERATURE 



CONDITIONS. 



In a previous paper 27 the characters available from cultural studies 

 of species of Penicillium were discussed. The series of observations 

 have been greatly extended in the three years intervening. These 

 characters may therefore be profitably reviewed, following the sum- 

 mary just given. 



Culture medium.- — The composition of the substratum is shown in 

 this paper to affect the character of the colonies grown upon it to 

 such a degree as to make the exact description of the medium essen- 

 tial. Examples of these effects may be cited to show how conspicu- 

 ous these differences may be. In a medium free from certain sugars 

 P. duclauxi produces upon the surface of the medium very short coni- 

 diophores with conidial fructifications, whereas when such a sugar 

 is added numerous coremia are formed, which in well-nourished colo- 

 nies often become 10 mm. in height. This species also produces a 

 rich purple color in certain media, but not in others. Hedgcock has 

 noted that P. aureum Corda (as distributed by him) produces colo- 

 nies orange-red upon alkaline media, but lemon-yellow in acid media. 

 P. digitatum Sacc. grows sparingly, if at all, in media offering 

 nitrogen only as nitrates, whereas many other species grow equally 

 well from nitrates and organic nitrogen. One species is included 

 which produces feeble gray or brownish cultures when carbon is pre- 

 sented from gelatin, starch, or lactose, but becomes a clear green 

 when cane sugar is added. 



A culture medium must offer not only the proper chemical ele- 

 ments for fungous growth, but must offer these in assimilable form. 

 Different species of Penicillium make quite different demands as to 

 the form of food substances required, hence a description must specify 

 the substratum accurately enough to enable the duplication of cul- 

 ture conditions. If, however, the proper substances in the proper 

 form are offered, changed percentages in the concentrations of these 



