Put them in peat soil with vermiculite, no heat underneath and natural light in a sunny window and they will be fine. I have read that Passiflora do not like coir but I have no experience of this.
Myles

Here is a link that might be useful: Seedling info

Thanks, Myles, will do. I've got peat and vermiculite on hand, so making the switch will be easy.....Do they need need a bit of fert, too? The peat and vermiculite don't have much to offer in the way of nutrients......BTW, the reason I used coir is because someone else on this forum touted its charms for germination. I can't argue with him----after soaking my seeds in tomato juice, they sprouted in just three days!......

No fertilizer needed, especially with P. incarnata that grows in very poor soil. Too rich nutrition will upset it. Peat will be fine. RE germination in coir..seed will germinate in anything if kept damp and warm e.g. kitchen roll on a hot window cill.
Myles

Thanks, Myles...One other quick question, if you don't mind. I've noticed that two of the seedlings are more yellow than green, which I suspect means they're trying to tell me something. Is that a condition that, with luck, will correct itself when I transplant them into the peat/vermiculite mix? Or is something that requires some other action to fix?

leave them to it. You usually get some weak seedlings. If they don't improve scrap them.
Myles

OK, many thanks, Myles!

I agree, -- p. incarnata is native in my area, have seen it growing wild. Just leave it be and it will come on, first year it may be spindly but will become robust shortly.

sandy