“What kind of bow can’t be tied?”/“A rainbow.”

A rainbow riddle is:
 
Q: What kind of bow can’t be tied?
A: A rainbow.
 
The riddle has been cited in print since at least 1943 and is popular on St. Patrick’s Day. The riddle has been printed on several images.
 
   
22 January 1943, The Age (Melbourne, Australia), “Guess These,” Junior Section conducted by Ralph Rover, pg. 5, col. 7:
What bow cannot be tied?—A rainbow.
 
5 March 1950, Lansing (MI) State Journal, “Young Folks’ Books Offer Fun in Plenty,” second sec., pg. 11, col. 3:
“What bow can;t be tied?”—“Rainbow.”
 
Google Books
The Giant Book of Family Fun and Games
By Jack Tedford
New York, NY: F. Watts
1958
Pg. 100:
What bow cannot be tied?
A rainbow.
 
25 May 1952, Leavenworth (KS) Times, “Riddles,” The Junior Times, pg. 17, col. 3:
What kind of bow cannot be tied?
Answer: A rainbow.
Janet Wikelski, 11,
1105 Metropolitan.
 
31 August 1958, South China Sunday Post-Herald (Hong Kong), “Heard these?,” pg. 17, col. 3:
Q. What bow cannot be tied?
A. A rainbow.
 
28 February 1962, San Diego (CA) Union, “Fun Time—The Riddle Box” by A. Leokum, pg. A10, col. 2:
What bow cannot be tied?
A rainbow.
   
12 March 1973, Austin (TX) Statesman, “Fun Time—The Riddle Box” by A. Leokum, pg. 36, col. 5:
What bow can’t be tied or untied?
A rainbow.
 
Google Books
Biggest Riddle Book in the World
By Joseph Rosenbloom
Illustrations by Joyce Behr
New York, NY: Sterling Publishing Company, Inc.
1976
Pg. 121:
What kind of bow can’t be tied?
A rainbow.
 
Google Books
Penguin Pocket Jokes
By David Pickering
London: Penguin Books
2006
Pg. ?:
What bow can’t be tied?
A rainbow.
 
Twitter
Mo.‏
@hey_molly
What kind of bow can’t be tied? A rainbow! :D
8:01 AM - 23 Apr 2009
 
Google Books
Happy Smile:
Jokes for Kids
By Adam Smith
Lulu Publishing (Lulu.com)
2017
Pg. ?:
Q: What bow can’t be tied?
A: A rainbow!