The stems of roses grown in hothouses for the cut-rose industry often are treated with a chemical that prevents rooting so that the blooms will last longer and the roses won't develop any "unsightly" roots in the vase.
Tiffany's absolutely right about the covered-wagon origins of this practice. The rose cuttings were plunged into potatoes for the long trip, but I'm sure the pioneers removed the roses from the potatoes before they planted them.
