The organza bags discourage pillage of your seed crop by both two legged and four legged thieves.
It lets (would be) thieves know that you want the seeds.

I buy mine online here, once Patti pointed it out. Minimum order sizes vary, around 10 to 30.

They have many different sizes and MANY different colors!

Best Organza: found by Patti1957
http://www.yourorganzabag.com/...

I claim male ignorance, and have never heard of organza before.

Does it still allow air movement, and how tight is the weave? Would it hold seeds of radish? lettuce? poppy?

I'm not absolutely positive about poppy seeds, but I've been planning to use organza "one of these years" to collect seeds from some California poppies that have been reseeding, but not as densely as I wish.

It would be smart of me to test some fabric and seeds indoors, first!

It is a "very fine" weave, I'd estimate maybe somewhere around 40 mesh or 60 mesh or even a bit finer. It lets air through very freely. It's intended to keep pollinating insects out, but I doubt it would keep pollen out for wind-pollinated species.

P.S.
http://www.giftsintl-us.com/pr...
Here is another source of organza bags. A few years ago, I thought that the first site had better prices, but I haven't compared shipping cost and minimum orders recently.

This second site also has a wide variety of ZipLocs, either 2 mil or 4 mil. Sometimes I use 3x4" Ziplocs or 4x6" ZipLocs to hold bundles of 2x3" Ziplocs with seeds.
http://www.giftsintl-us.com/ca...

I like big glassine envelopes/bags better for holding bunches of 2x3" Ziplocs, but the only really big, gusseted glassine bag I bought was TOO big for my relatively small tubs.

Organza bags work for poppy seeds.
And, yes, they do allow air circulation.
I dry poppy capsules in them.
You can see through the bags.

Thanks, Caroline.
I did have a chance to stop in at a Jo Anne Fabric store to see.

I'm sure the bags work excellently!