Maeve, I found nothing at all about any apple called a gentian, early or otherwise. I did, though, find an antique apple variety on foodhistory.com's "A Is for Apple" page whose name sounds as though it could have mutated into "gentian":

"Ginet (AKA Genet, Geneton, Geniton, Gennetin, Genneting, Gennetting, Indiana Jannetting, Janet, Janetting, Jefferson Pippin, Jenetings, Jeniton, Jenitons, Jennett, Jennette, Jenniton, Missouri Janet, Never Fail, Neverfail, Rall's Genet, Ralls Genet, Raule Jannet, Raule's Genet, Raule's Janet, Raule's Janett, Raule's Janette, Raule's Jannet, Raule's Jannette, Raule's Jannetting, Raule's Jennetting, Raul's Gennetting, Rawle's Genet, Rawle's Janet, Rawle's Janett, Rawle's Jannet, Rawle's Jennet, Rawle's Jenneting, Rawle's Jennette, Rawl's Janet, Red Neverfail, Rock Remain, Rockremain, Rock Rimmon, Rockrimmon, Royal Janette, Winter Genneting, Winter Jannetting, Yellow Jannett, Yellow Jannette)

"This apple was first propagated in the United States from the farm of Caleb Ralls in Amherst County, Virginia. Ralls may have worked with clippings brought from France by Edmund Charles Genet, French ambassador to this country, at the urging of then–Secretary of State Thomas Jefferson, around 1800. Medium-sized yellow apple, covered and striped in varying shades of pink and red. Crisp, juicy, and tender."

None of the pseudonyms are "early" anything, though. Good luck finding your apple!

Claire