RESISTANCE OF MOLD SPORES TO SUNLIGHT 59 
doubtless this is true in a measure, but there still remains the 
fact that Oidiwm with colorless spores also shows remarkable 
resistance. 
The fact that mold spores are relatively lighter than other 
spores would suggest that they have succeeded better in elim- 
inating water from their protoplasm and hence are better able 
to resist adverse agents. How far this may really enter into 
the explanation it is difficult to say. 
The results help to explain the prevalence of mold spores 
in air where they greatly preponderate over bacterial spores. 
While bacterial spores can resist the action of sunlight but a 
few hours, mold spores can resist this action for days. Indeed, 
it is doubtful whether sunlight is able to kill mold spores. 
SUMMARY 
Spores of the following molds were exposed to direct sun- 
light on paper slips in glass petri dishes: Mucor Asper- 
gillus niger, Aspergillus fumigatus, Aspergillus nidulans, 
Oidium, Penicillium glaucum. The results show that mold 
spores are able to withstand 58 hours or five days of continual 
exposure to the intense rays of a summer sun. 
Apparently, sunlight possesses slight, if any, germicidal 
powers upon mold spores. This fact helps to explain the 
greater prevalence of mold spores than bacterial spores in 
air, for the latter are killed usually within five hours. 
