I enjoy questions like this myself and hope for hearing or finding answers. In my *guess*, the trait is dominant. I do a lot of dabbing, but not a lot of growing out the seedlings. I really like watermarks but haven't grown out hardly any seedlings from my plants with watermarks. But the daylily Jennifer Trimmer came to mind. (Don't have time to check Born to Run.) So I checked the database here to see how many children have been registered with Jennifer Trimmer as the parent. As I had hoped, not too many, so I looked at every child plant. Every child plant had the watermark trait. But I didn't look at every single parent that Jennifer Trimmer was crossed with. On quick glance, most also had a watermark with the exception of one or two. So just to get some statistics, one might do the same with several daylilies that have a watermark. So then it would also be interesting to see how many watermarks were produced by daylilies with [no watermark X watermark] or [eyed daylily x watermark]. Do eyed dayliles x watermarked daylily produce a watermark or a pattern?
