The erythroniums of Japan and Eastern North America have immature embryos
when the seed is shed. I found the following paper very interesting.

Ecophysiology of seed germination in Erythronium japonicum
(Liliaceae) with underdeveloped embryos
http://www.amjbot.org/cgi/content/full/89/11/1779/
by Tetsuya Kondo, Nori Okubo, Taku Miura, Kazushige Honda and Yukio Ishikawa.

They tested many variables and combinations of variables - constant,
alternating or variable temperatures, and light.
They had many lab experiments, and also outdoor pot experiments.They
didn't just observe the outside of the seeds, but also sliced them open to
see what was happening to the embryos.

They found that Erythronium japonicum seeds are not able to germinate
as soon as they are shed, because the embryos are immature. They require a
hot period for the embryo to lengthen, then a cooling period for germination.
Seeds would germinate if given 90 days at 25C, then 5C, or if they were kept
around 10C (or 15C days/5C nights). They did not germinate if kept at these
temperatures: 0=B0, 5=B0, 15=B0, 20=B0 or 20=B0 days/10=B0C nights .

In nature, the seeds have germinated by November, and seedlings emerge
as the snow melts in spring.

There are other species that also have immature embryos, E. albidum,
E. grandiflorum, E. americanum, and E. rostratum. Their temperature
requirements differ, and their embryo elongation is either later, or
carries on later (closer reading of the article needed here.)

The bibliography lists papers on germination of these Eastern U.S. species.

Diane

one concern is not knowing how long to maintain the bulbs at warm temperatures after the leaves die down before beginning vernalization. Given the natural range of E. multiscapideum (PBS wiki lists as E. "multiscapoideum"), there is a possible minimum time requirement for warm dormancy, which likely varies with temperature, before the bulbs can perceive vernalization. While there is some literature on this topic for other species (especially Lilium), I can't find any dormancy info for Erythronium. As for vernalization, ten weeks at 5C has been reported to be the optimal vernalization period for Erythronium 'Pagoda.'