Never tried to grow it from seed but according to my info it says Hardy Perennial, 30-270+ days for germination, temps of 70-75F, well drained soil, surface sow and pre-chill for 2 weeks.

Many clematis specially large flowered ones will take a year or more to germinate. You might want to place your pot in the plastic bag and keep it outside. See winter sowing forum for details. Clematis tangutica, alpina and macropetala and species will germinate sooner. Germination often irregular during several months.

Roberta, you mention refrigerating the seed but you don't say if moist...dry chill is just storage.

Knowing which clematis might help -

Druse: Clematis - Moist cold 2 - 6 months depending on the species, followed by sow 70o for germination in 30 - 365 days, again depending on the species

This site is often mentioned on the Clematis Forum as having good information -

Here is a link that might be useful: Clematis from Seed