Just go ahead and try it, as somebody else may not have any luck with it, you may have.
Pollen should be OK, but the question is, does it set seed, (hips)??

very very tiny to get pollen from!
However, tiny roses are useful for breeding. One of the best landscape roses, Purezza, was made by crossing the micromini Tom Thumb with a white Lady Banksia. So even the most bizarre crosses can be useful.

Hi Bellegallica,

I tried it couple times. For me, it would start to make hips, but they would fall off a couple of weeks after I made the cross. As for the pollen, I didn't have any luck, but I was using tetraploids, and I think that Si might be a diploid.

What I did was wait a day after the anthers changed color and then used tweezers to remove the petals and used the stem as a paintbrush on the parent flower.

Good luck!

Marbree

Thanks for the responses. Marbree, I had the same idea of just holding onto the stem of the flower rather than trying to hold onto such tiny stamens.

Is there some literature you could point me to as far as the tetraploid/diploid stuff? I'm unaware as to which crosses will definitely not work according to chromosome counts.

Hi again Bellegallica, the only source on ploidy that I know is from Paul Barden's web page Old Garden Roses and Beyond:
Species and Group Ploidy list by David Neumeyer
http://www.rdrop.com/~paul/species_ploidy.html

The parentage of Si is listed at Help-Me-Find Roses and it shows a lot of the polyantha and miniature chinas (both are generally diploids) in it's background:
Si at HelpMeFind Roses
http://www.helpmefind.com/rose/pl.php?n=5751

Hi is another rose of a similar size to Si, but I have no idea as to it's ploidy and have never tried it. It might be also fun to work with.
Hi at Paul Barden's site Old Garden Roses and Beyond
http://www.rdrop.com/~paul/minis/hi.html

Marbree

Sorry, I missed part of your question. Basically they say you can use a higher ploidy pollen on a lower ploidy seed parent, but the reverse doesn't work.

For example, they say you can put tetraploid (4 genes) pollen on a diploid (2 genes) seed parent and get triploid (3 genes)seedlings, but the reverse won't turn out very well.

I hope I've said this clearly, if not, let me know.

Also, I think that I heard once that the very tiny minis like Si might be poor seed setters, but I'm not sure.

I really wish you luck on this, and hope you're the one to make it work.

Marbree