Most likely the seed pod.

I didn;\'t know they grew from seed. Do I let the pod dry out on the stalk or can I remove the pod and dry the seeds that way?

Iris cultivars do not grow true from seed. Each different seed in each different pod will produce a different iris (the seeds that manage to germinate, that is), none of which will be identical to the pod parent. That's how iris hybridizers create new irises.

If you want to try growing irises from seed, allow the pod to ripen on the plant until it starts to turn brown and splits open at the top.

Laurie