Answer: According to the Thompson & Morgan Successful Seed Raising Guide, hosta seeds can be placed in a plastic bag with some barely damp soilless mix or peat moss and kept in the refrigerator for several weeks to provide a cool stratification period prior to planting (or they can be planted outside in the fall). Check them periodically for swelling or signs of sprouting. After planting in a moist yet well drained mix, the seeds germinate at a cool soil temperature (55 to 60 degrees), and may take 30 to 90 days.
According to the above, general instructions for Arisaema indicate the seeds may take between 30-180 days to germinate, also at a cool temperature of 55 to 60 degrees. The seeds require light to germinate and should be planted lightly in a well drained mix.
You might also find the following article by Tony Avent of interest as he addresses your plant:
Arisaema, Arisaema, Arisaema(Cobra Lily, Jack in the Pulpit) at http://www.plantdel.com/JCMax/olcarisa.htm and may also want to look into information available through the International Aroid Society at http://www.aroid.org/ since your seeds are from Japan rather than the typical wildflower.
Good luck with your seeds!
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