The orchid seed has a small embryo within an air-filled hull, the Testa. When a seed falls onto a good place, the Testa rots away and the embryo can be infected with the mycorrhiza fungus. In culture on artificial soil, the Testa is sometimes removed with a mild desinfectant which also removes unwanted fungus spores. 20 minutes in a 0.5% Natriumhypochloride solution should do the job.

Asymbiotic culture on an artificial soil can simulate the mycorrhiza. Anyway, the seed takes some time before it develops roots and leaves. One or two years it grows subterranean, this is called the Protocorm stage.

Some more interesting things about seeds:

The seeds and husks of the tropical Vanilla planifolia come from the only orchid which is grown in culture for culinary purposes.

The tropical Anguloa has the record with 4 millions seed per husk.