In this study, 95 previously dry-stored (for 4 months) R. multiflora achenes were continuously water soaked in a glass of tap water at room temperature.
There were 12 radicle sproutings in the glass of water. Upon sowing these, 11 germinated into seedlings and one did not. One of these 11 seedlings had only one cotyledon, and I eliminated it. The remaining 10 seedlings are thriving.
I randomly ended this study at ~day 70 of water soaking, since at that point in time I guessed there would likely be no additional radicle sproutings.
This rate of germination (+/- 10%) is similar to the rate of normal embryos I have counted when I randomly embryo-sampled some achenes of this clone.