Would mullberry make a good self bow? How about sassafrass? I have pieces of each big enough to make bows from.        

Both will work.

My favorite selfbow to date is a mulberry. Treat it like osage and get down to heartwood, just make it a little wider than you would osage.
 I have had 2 failures with sassafras, but I won't give up on it yet....Sassafras is called a great bow wood in (I think it was) the Witchery of Archery.
 Good luck...Terry

"The Osage orange (sometimes hyphenated) or Osage apple or simply Osage (Maclura pomifera) is an ornamental plant in the mulberry family Moraceae."

I would think mulberry would work.

Mulberry is good. It is used as the center lam on bamboo japanese bows. I have seen one mulberry self bow and it was a great shooter. Lighter and not quite as hard as osage, but very fine bow wood. I have heard of sassafras bows, but not seen one.

http://www.murraygaskins.com/mulberry.html

This should answer your question rather well.

Thanks Isihiwannabe.That was a good read.  

Mulberry is a joy to work with.... Slightly wider in the mid-limbs... I enjoy using it for my sinew recurves as well... Is it as good as Osage... Everyone will have a different answer for you... Good luck...