Subject: Why isn't my bread molding?

I'm doing a science experiment on mold growth on bread.  I'm trying to figure
out if different temperatures affect mold growth.  I'm using wheat bread (with
preservatives) and bread with no preservatives.  I let all the bread be exposed
to air for 30 minutes.  I put all the bread in separate zip-lock bags.  I put 3
of each kind of bread in 3 different locations: in the refrigerator, in a room
at room temp., and outside.  My problem is that the wheat in the room hasn't
molded and it’s been about 30 days.  I have no clue what I did wrong.  Do you
think that the bread just won't mold or is something wrong?  Thank you for your
time!  

Re: Why isn't my bread molding?