Don, the backing is probably paper. That was a common backing years ago. I have a few lemon wood bows made by York Archery from the 1940. York and other wood bow companies used Fibre backings on some of their bows. This fibre was a compressed paper product that for York at least came in white or black.
Does the crack run across the bow or lengthwise? If it is across the bow on the belly side it is a fret(chrysal)and is unfixable. It is common for old glue lines to dry out and come apart like with this riser. All of this can be fixed with exception to a fret in the belly.
If you want to be able to shoot this bow you will have to reeducate it how to bend again. It's just like the initial tillering where you exercise the limbs gradually until you get her back to full draw. This can go either way though!
For me, these old bows have more of a historic value so I just hang mine on the wall to admire a part of our archery history from the golden age of American archery. It is not worth the risk of distroying one of these bows just to be able to shoot it. As a collector item anything you do to "improve" your bow will take away from it's value. IMO