For a time, from the mid 1920's to 1930's, there were two versions available of The Land of Oz. The "regular" edition, which contained 12 color plates, and the "popular" edition which only had a color frontispiece. The popular edition cost a dollar, as opposed to the $1.60 or so that was charged for the standard edition. When color plates were dropped from the books in the mid 1930's, the popular editions faded away.
The popular edition was clearly identified on the front cover - but the words pop up in a variety of places! Above, you can see a couple versions, taken from the Internet. In 1939, another popular edition was released to capitalize on the 1939 film of The Wizard of Oz. This time, the book was given a new cover and larger format - but the price remained the same.