Japanese maple, Acer palmatum, and their hybrids especially, often have multiple germination inhibitors. These must be broken down in order for them to germinate. These are most commonly broken down by either warm moist pre treatment or cold moist pretreatment. The easiest way to do this is to keep them moist (not wet) in a ziplock bag and give them alternating cold/warm pretreatments. If they have already had cold/moist (as the seller infers), then keep them at 70F and moist for three months. Watch for signs of germination. If any germinate, remove them, but keep going with the process for the others. After three months warm, give them 3 months cold in the refrigerator. Again, remove any that germinate. After 3 months, return to warm/ moist for 3 months, keep doing this until all have germinated, or the seed rots.
To test seed, cut a few open with concave cutters to inspect the kernal. It should be creamy white and solid. If it is watery, or dark, then it is rotten. If the first few are rotten, keep going to see if you can find any viable ones. If you find about 20 bad ones with no good ones, throw the lot away. Dissectum seed is always difficult and not worth the effort in my opinion. The offspring will not be 'Viridis' and will show variable leaf shapes if they do grow they will be curiosities only. If you want cultivars, buy grafts, or better yet cutting grown plants if you can find them. If you just want good old solid Japanese maple for bonsai, stick with species green seedlings, or collect the seed yourself. Fresh green species seed will almost always germinate in high percentages after a single cold/moist treatment; I have grown thousands of them.
I once went through this whole process with some A. palmatum x japonicum hybrid seed and it took two years for most of them to germinate.
For more information on seedling propagation see this article at my website:
http://www.evergreengardenworks.com/seeds.htm
Brent
EvergreenGardenworks.com
see our blog at
http://BonsaiNurseryman.typepad.com