Guest Pedant Alert: "his" is a possessive pronoun without apostrophe. For that matter, "her" is another. If you're going to be a pedant, you really must take care to be right as well.

CrazyEddie, "greengrocer's" is NOT a plural.

weelittledrummer, it's because you're a plural that you can't have an apostrophe. (You could think about giving yourself an initial cap though.)

Giok and Kendall, I expect you're remembering that "Lords Justices" is correct, though encountered only in the judiciary of England and Wales.