Peck & Co. v. Lowe,
247 U.S. 165 (1918)  page 172-3

•  ”The Sixteenth Amendment, although referred to in argument, has no real bearing and may be put out of view. As pointed out in recent decisions, it does not extend the taxing power to new or excepted subjects, … Brushaber v. Union Pacific R.R. Co., 240 U.S. 1, 17-19; Stanton v. Baltic Mining Co., 240 U.S. 103, 112-113."