The seedpods on this pair of Mammillaria sp. (probably matudae) have been slowing ripening for the past month, and I've already collected many dried seedpods for possible future propagation.
I say possible because I've never been big on seed propagation. It takes several years of work and care for seedlings to grow to the point of flowering, and I've never had the patience for it, but after my recent success with Coral Aloe seed propagation, I may try my hand with some of the cactus seed I've collected this year.
The initial problem with sowing seed is separating the tiny seeds (each about the size of a grain of sea salt) from the pulp found inside the pods to prevent rot. The seedpods I've collected from these Mammillaria really aren't that difficult because the pods dry and then it's just a matter of splitting the pod and spilling out the seeds into a container. With other genera, the seedpods, or fruits, are sometimes a lot larger and filled with mucilaginous pulp. Trying to separate the seeds from pulp in those larger pods is impossible for me to do. I'm just too impatient.
An M. matudae specimen in a four-inch pot is available in any local nursery for about $1.99. When I think about that, I really wonder if it is worth my time and effort to sow seed. Perhaps not.