The source regarding scent is the Stimart and Boyle article referenced in The Zinnia Breeder's Handbook that you mentioned you have.
Lots of flo era don't have scent. There are several theories about how bees find flowers. They include visual cues (bees see at a different spectrum than we do, according to my bee keeper friend. David Attenborough did a special about bees and talked about he protons they pick up while they fly and the negativity charged flowers which are grounded. He liked them to opposite magnets, essentially. Maybe bees can't smell?!
