It just happens that some seeds from some good reason do not germinate. Won't happen again, I hope.
But you have that Hoodia, it is precious plant, and I wish you good luck with it!
I had only one, once, that I received as a gift, and I killed it :( , but now I want, just as you did, to purchase some good seeds and grow it from beginning to get know with that plant better.
I was surprised to see that the Hoodia actually did well in cooler temperatures. I think it must be treated like a cactus only when it is older. I never had these on the heat mat although I did have them outside when the ground was very warm but brought them inside once they started germinating
I just wrote in my tips-notebook those your experiences with Hoodia. :)
I will need them, hope very soon :)
:-) Good luck!