Passion flower seeds:
Gardeners and collectors grow passionflowers from seed, the flower seeds can be slow to germinate. There is actually a chemical in the seed to keep germination slow.
The inhibitors stop the seed from germinating too soon, e.g. while still inside the fruit, inside an animal’s digestive system, over winter or while it is too dry or cold. The most common inhibitor in temperate plants is abscisic acid, a plant hormone, which induces dormancy in the embryo.
It is recommended to scarify the seed and then soak it for 24/36 hours in a citrus juice such as lemon or passionflower. Plant 1/4 inch down in good compost or potting soil. Plant on carefully when there are two true leaves.