This seems to be a common question. Because my floors are so dark I'm not quite sure which are the medullary rays and having a hard time telling. Floors are probably circa 1908. Since my house is under remodel I don't have access for great pictures but here is a smattering I was able to find from various other purposes: Google photo album

Thanks! Trying to match in addition but not sure which it is! Attached a few below in case you don't want to click the link.