92 CULTURAL STUDIES OF SPECIES OF PENICILLIUM. 



completion of the typical colony. The figures are brought together 

 in Table 6. 



Data at 20° C. — The data at 20° C, as given in the first column of 

 Table 6, are regarded as typical for the species studied and given as 1 .0. 

 Numerous series of cultures with all these forms under close observa- 

 tion in the incubator at 20° C. and in the laboratory where the tem- 

 peratures used ranged from 15° to 25° C. or slightly higher have given 

 approximately the same results. Within these limits, rise or fall in 

 temperature affects the amount of growth or the stage of develop- 

 ment of the colonies within a specified time without affecting the 

 character of such growth. The differences between cultures grown at 

 different temperatures within these general limits are quantitative, 

 not qualitative. Unless made for a specific purpose cultures of these 

 fungi may be safely grown outside the incubator without affecting 

 their character, since the conditions in the ordinary working room are 

 approximately those furnished to these forms by nature. 



Data at 37° C. — At 37° C. thirteen forms showed normal develop- 

 ment. Of these seven grew better at 37° C. than at 20° C, this 

 number including but one well-known species — P. luteum. At the 

 same temperature the spores of seven species were killed, including 

 among these P. italicum and P. digitatum, the species destructive of 

 citrus fruits. Of the green forms abundantly found, only one grew 

 well at 37° C. — P. chrysogenum. The numerous green forms studied 

 were not killed, but simply prevented from growing by the heat. 

 Every form except those noted as killed developed normally in the 

 same tubes as soon as cooled to 20° C. 



Ice thermostat. — In compartment 1 of the ice thermostat, ranging 

 from 0.5° to 2° C, 20 of the forms experimented with either produced 

 germ tubes only or failed even to germinate in twenty-nine days. Of 

 the remaining 18, only 6 produced colored conidial areas in that time. 

 Several other species produced considerable masses of white mycelium. 



In compartment 2, ranging from 3.2° to 6° C, with an average 

 slightly above 4° C, 16 or 17 still showed germination only or com- 

 plete inhibition; 11 showed colored conidia; several additional forms 

 had germinated or produced distinguishable mycelium. 



In compartment 3, with an average temperature about 7° C. and a 

 range from 6° to 10° C, 16 forms produced colored fruit. Of these, 

 9 had reached the typical appearance of mature colonies of the species 

 within the 29 days. Nine only remained without showing some 

 mycelial growth in addition to germination. 



In compartment 5, averaging about 9° C. and ranging from 7° to 

 10.5° C, all species had germinated and all but one had produced 

 mycelium; 25 forms had developed colored conidia; 17 had produced 

 colonies of typical appearance. 



