Poppagator had it right when he said:

Strunk and whatzizname's "Elements of Style" probably will verify this; that's the main "rulebook" we used.

Strunk & White, in The Elements of Style (a/k/a "The LITTLE Book") give a series of succinctly phrased rules.

The VERY FIRST rule given is (fairly close to verbatim) as follows:

"1. To form the plural of a singular noun, add apostrophe and S, regardless of the final letter. Thus, 'the witch's curse'" (and a few more examples). "Exceptions are such ancient names as "Jesus' teachings" and "Moses' laws."   

Even with the ancient names, S&W looked with favor on recasting the sentence to refer to "the teachings of Jesus" and "the laws of Moses".

E. B. White, by the way, was seriously referred to as "The best writer in the English language." You're entitled to prefer some other writer, of course, but that's still a fast league.

Dave Oesterreich