These pictures are from the wood flooring above the basement of a home built in 1930. What exactly is this white substance on the wood?
Looks like white mold or the start of dry rot in the framing.
Some sort of fungi caused by the excessive moisture environment.
The wood looks like it was treated with creosote, which was a common way to do pest control years ago. You may want to add a disclaimer about that chemical possibly being present.
I agree…the white stuff looks like mold.
White rot… most likely started, died out if not enough moisture was present. In spore form it will stick like glue to the surface, waiting for moisture.