3¢ Portrait of Whistler's Mother - Mother's Day Stamp - Issued without Gum
The flat plate and rotary issues can be separated as normal, the flat plate stamp is perf 11 and the rotaty stamp is perf 11 x 10½. If the stamp is imperforate it is the Special Printing, Number 754, and flat plate. Although the Farley reprint appears to be the same shade as the rotary stamp, any difference in shade is incidental.
The Farley printing was issued without gum as a sheet of 200 stamps, printed by the flat plate method, with four panes of 50 separated by guide lines. In the very center of the sheet the horizontal and vertical guide lines crossed, collectible pairs and blocks with guide line between, as well as a center-line block. The margins of the sheets had arrows at the end of the guide lines, creating collectible arrow blocks.