I think it belongs to the cryptic part of 25a: rum is the spirit My! = gracious and gin = cotton fbre separator - there is a similar def in Chambers under gin 2 at the end after the "trap" bit - ... " to clear of seeds by a cotton gin"
Complete except for 1A and 2D. 1A looks as if it should be TRANSECTS and 2D as ANTLIAE but can't really make sense of them. Any hints gratefully received. Thanks for all the other hints which gave me a start on this one, otherwise I don't think I would have made a start after reading the preamble.