Cachinnagenic or cachinnogenic

There is this funny word cachinnogenic that Wodehouse used in America, I Like You p. 161:

[...] it used to be obligatory to laugh whenever anyone on the television screen mentioned Brooklyn. If there was one credo rooted in the minds of the citizenry it was that the word Brooklyn was cachinnogenic. And now there has been a shift in the party line, and today you have to laugh at Texas.
Nobody knows why. It is just an order that has come down from the men higher up. It is perfectly permissible under the new rules to keep a straight face when somebody speaks of Oshkosh, Kalamazoo or the Gowanus Canal [...]

But the Punch article from which this chapter is adapted ("This Happy Breed of Men", June 1, 1955) reads cachinnagenic instead.

Of the two, cachinnogenic is more correct from a linguistic point of view, since the word is composed of Latin cachinnus "a laugh, esp. of a loud or boisterous kind, guffaw" and the suffix -genic, which makes the whole mean "productive of (loud) laughter". But there is no reason for a Latin noun of the second declension to produce compounds in -a-: for that you need to have with a noun that ends in a, like mediagenic "attractive as a subject for reporting by news media".

Now, cachinnagenic is interesting because it leads (via a Google search) to Wodehouse's probable source for the Punch piece. This was an article titled "Analysis of the Boffolo Texensis" by Stanley Walker in the New York Times, March 12, 1955. Walker writes:

Texas has become the most cachinnagenic (chew on that one a while, you microcephalic Yankee hyenas) of the American states, clearly outdistancing Arkansas. The belly laugh at the expense of the Lone Star State (boffolo texensis) has made the customers with a low titillation point forget Gowanus, Walla Walla, Bridgeport, Oshkosh and Kalamazoo.

(A captivating essay about Walker and his native Texas is "Stanley Walker: The Retread Texan" by Jay Milner available here.) Both the argument and the examples given (as well as the dates) point to a derivation between the two. Wodehouse seems to have taken the word from Walker with a, and somewhere along the process of preparing the text for the book either he or his editor corrected a to o.

The story of the word and its correct application to American toponymy didn't end there. In Variety, Jan 9, 1957 one sees an ongoing discussion as to whether Texas had really dethroned Brooklyn.

It is likely that Wodehouse knew about Walker or even met him, although the only shred of evidence of any contact between the two I've found so far is the following mention in a letter to W. Townend (December 1934 in Performing Flea, or September in Author! Author!):

Then I had a cable from the Herald Tribune which said, "Happy about Lord Havershot"—that was the name of the hero of the novelette—from which I inferred that it was all right. But I do hate these ambiguous cables. I mean, the editor might quite easily have written "Not happy" and the French postal officials might have cut out the word "Not" as not seeming to them important. Finally, however, a letter arrived, just about the time I heard the news of the success of the show, saying that they liked the story.

Walker was still editor of the New York HT during this period, so he was probably Wodehouse's correspondent.

Be that as it may, the next time you want to describe Gussie Fink-Nottle's prize-giving scene as "productive of (loud) laughter", you need no longer hesitate between the two spellings.