It concerns the opinion of Naudin and Darwin that a single pollen grain does not suffice for fertilization of the ovule. I used Mirabilis Jalappa for an experimental plant, as Naudin had done; the result of my experiment is, however, completely different. From fertilizations with single pollen grains, I obtained eighteen well-developed seeds, and from these an equal number of plants, of which ten are already in bloom

Letter VIII, July 3rd, 1870. - Letters to Carl Nägeli