Many of the jō-stems of Germanic were in fact ī/jō-stems that go back to ablauting iH/ieH-stems of Proto-Indo-European. The Germanic wō-stems go back to pieuH/ueH-stems with parallel ablaut behaviour to the iH/ieH-stems. Whereas the suffix variant in -ū has nowhere been preserved as such in Germanic, some traces of ablaut and accent variation remain in the Germanic wō-stems. Some such traces were first identified by Kroonen (2013); in this paper, the authors present a more detailed collection of the evidence for ablauting uH-stems in Germanic.
HansenBjarne S. S.Layers of root nouns in Germanic: chronology, structure and originEtymology and the European Lexicon Proceedings of the 14th Fachtagung der Indogermanischen Gesellschaft17–22 September 2012CopenhagenWiesbadenReichert169182Forthc
LubotskyAlexanderJamisonS.MelchertH. C.VineB.The Origin of the Sanskrit Roots of the type sīv- ‘to sew’, dīv- ‘to play dice’, with an Appendix on Vedic i-PerfectsProceedings of the 22nd ANnual UCLA Indo-European Conference2011BremenHempen105126