Well spotted Terry!
There's a fascinating and comprehensive 1923 book on making crystal sets, with full constructional details. It also has a diagram on page 122 showing a graphical method of memorising Morse. Clever though it is, I'm not sure it would have helped me when I learnt Morse. In the end, you just get to know the rhythm of letters and familiar words such as 'the' or 'feet' and terms such as the well known 'best bent wire' can be understood at speeds much higher than we're capable of sending.
I guess that if the graphical method had caught on, by now it would be very familiar.
Here's the link to the crystal set book:
http://www.jumpjet.info/Pioneering-W...rity/1923e.pdf