These stories are additions to the Mushroom Planet Series that is made up of "The Wonderful Flight to the Mushroom Planet" (1954), "Stowaway to the Mushroom Planet" (1956), "Mr. Bass's Planetoid" (1958), "A Mystery for Mr Bass" (1960), and "Time and Mr. Bass" (1967). The first story could have happened almost anytime in the storyline, but seems to fit best between books 2 and 3. The second story seems to fit in somewhere between books 3 and 4. These stories could have been written especially for the Reading Round Table books, or may have been material edited out of previous books. The Reading Round Table is a supplemental reading series for schools made up of short booklets. The booklets are grouped into various colored series of different reading levels. This booklet is from the Grey or Silver series. This book has the code "1 3 5 7 CL 8 6 4 2" on the inside of the front cover. I believe that this code with the 1 in the sequence indicates that the book is a first printing.