Grosset & Dunlap "breeder" set

This is an interesting format, as it was only used for the first three books, around 1937.  I call it the "breeder set", as that is the common term for the first 2 or 3 books of a series that tend to be issued at the same time to gain interest in a new series.  Of course, by 1937, this was no longer a "new" series, but G&D decided to issue this set of three with orange cloth covers and standard cover illustrations.