Dear Marsha,
I had the same thought as Mona, though I am no expert. I was thinking probobly had to do with a Phonetic spelling of the surname, though I am not sure how Bohne is/was pronouced. As I have a Bohne/Bohn/Bone showing up in St. Louis records. Thought maybe pronouced Bon-nee, which I think could maybe be pronouced Bay-nee depending on the nationality of the person pronouncing, and there was lot of different immigrant peoples in that time periord, especially in the midwest. Irish, German..later Polish, Italian...etc. I wonder if the pronounciation would differ depending on the part of Germany they may have have come from? I don't know.
Not sure in your case, but I know for a fact some of my ancestors cound not read or write, so they had to trust priests or other officials record keeping and it's the recorders spelling ability that is reflected in the records we look at today.
My greatgrandmother for example born in Washington County, Illinois in 1888 never learned to read or write, and I don't think it was that unusual even as late as that for farm families, especially for the females.
Even one of our greatest presidents Abraham Lincoln had no formal education.
Barbie
St. Louis