The turnip story ("How I edited an Agricultural Paper Once")
appears in _Mark Twain at the Buffalo Express_, and also in
Lou Budd's anthology--I, too, have no recollection of
potatoes, unless he incorporated a story like that in
_Following the Equator_.  It's been a while since I read
this, but it was an eclectic collection of set pieces along
with his descriptions of the places he visited, and included
the Pudd'nhead Wilson's New Calendar...best of luck in
researching this.

Jan McIntire-Strasburg