Umm, the short form?
Anything that gets them there is fine.
(Sending seeds in a thin, flat, First-Class Letter envelope only works if it never goes through a big or modern sorting facility. Those have very high-speed rollers that could hardly have been better-designed to crush seeds. You might get lucky if you tape the seeds in the very
middle of the envelope, because (usually?) the rollers only grip the top and bottom thirds or quarters of the envelope. Padding inside the FC Letter envelope MIGHT help, because I have gotten some tiny seeds that were crushed enough to embed them in the Zip-Loc plastic, and put permanently-visible dents into the plastic Zip-Locs, but not QUITE crushed.)
I can't keep it simple even when I try!
