These are fragrant Stock seed pods. I started the plants from seeds collected last year, and they have done fairly well this year.
If you start them indoors in a little greenhouse box (the type with transparent plastic cover – I strongly recommend it, it accelerates the growth of plants in a manner that is nothing short of miraculous) you should have big and strong seedlings to plant in your garden after the last frost.
The flowers came true from seed, exactly like their parent plants, including the color.
Keep seeds in paper bags, in a dry, cool place.
This is what the flowers look like: