The next couplet was also used as an autograph-book rhyme:

Think of me when you are happy.
Keep for me one little spot.
In the depth of thine affection,
Plant a sweet forget-me-not.

--from the autograph book of Mary Belinda Riley, 1882.

Also quoted in the book "Hill's Manual of Social and Business Forms: A Guide to Correct Writing," by Thomas E. Hill, 1884, which you can see at Google Book Search.

[Also found at a few other paces on the web.]