Q: I have perfectly round brown dots on the underside of some of my Boston fern leaves. I can scrape them off with my finger nail and it leaves an indentation of the same size in the leaf. They look like poppy seeds.
A: The dots are called sori. They contain the reproductive spores of the fern. Since ferns do not have flowers, they scatter spores instead of seed.
Fern enthusiasts collect the tiny spores and dust them onto the surface of a brick that has been almost totally submerged in a pan of water. They then cover the pan with a clear plastic bag.
The spores sprout and form a small, heart-shaped prothallus. The prothallus produces two different cell masses, one of which produces fern sperm and the other of which produces an egg. When an egg has been fertilized, it gradually grows roots and fronds, which lead to a new fern.