INCUBATION EXPERIMENTS. 91 



as completely as possible. Carbon dioxid washed through water and 

 through sulphuric acid was carefully introduced. The exhaustion 

 was repeated and the gas introduced a second and a third time. The 

 cultures were then permitted to stand one week and examined. A cul- 

 ture of Oidium lactis among the species of PenicHUium was found to 

 have grown some. No species of P< nidUium had produced a colony. 

 The carbon dioxid was then three times exhausted and replaced by 

 air and the jar permitted to stand a second week. Normal colonies 

 of every species were produced. Clearly, therefore, no one of the 

 species of P< niciUium under experimenl was capable of grow Lug in an 

 atmosphere of carbon dioxid. and no species was killed by exposure 

 to such at mosphere. 



INCUBATION TESTS. 



The importance of temperature in determining the distribution of 

 fungi in nature, and in controlling their presence in the household, t be 

 dairy, and the storage room, made the determination of the limits of 

 temperature for the growth of these species desirable. The following 

 incubation experiments were therefore made. (See Table 6.) 



1 . Incubation at 20° C. Tbis was repeated several times with fully 

 checked records. 



2. Incubation at 37° C. (range of variation 35° to 38° C.) for six 

 days; cultures then examined, recorded, and the incubator cooled to 

 20° C. for the succeeding six days. 



3. Use of the iee thermostat. Four series of cultures were made 

 in bean-agar with 5 per cent cane sugar — a medium adapted to pro- 

 duce typical colonies of all species in a minimum of time. The tem- 

 perature of the incubator was recorded eight times a day at three- 

 hour intervals. The range of temperatures in the compartments 

 used and the average of fifty-five observations taken in the first seven 

 days were as follows: 



Compart menl I, average 1.05° C, range 0.5° to 2° C. 

 Compartmenl 2, average 4° C, range 3.2° to 6° C. 

 Compartment 3, average 7° C, range 6° to 10° C. 

 Compartment 5, average 8.7° ('., range 7° to 10.5° C. 



Observations upon the cultures were made by the writer at 3 and 



7 days and repeated, by the kindness of Miss Lucia McCullough, 

 of the Bureau of Plant Industry, at 15, 23, and 29 days. For con- 

 venience of comparison, the notes from all these observations have 

 been reduced as fairly as possible to a decimal code, iii which ger- 

 mination of conidia w it houl furl her growth is given as 0. 1 and typical 

 colonies at l.Oj fractions from 0.1 to 0.7 represent vegetative 

 mycelium without colored conidia] areas, and from 0.7 to 1.0 the 



" I '>> the courtesy of Dr. Envin 1'. Smith the ice ilicnuostat of the Bureau of Plant 

 Industry of the United States Department of Agriculture was placed at my disposal. 

 It was iced and regulated under his instructions. 



