NOTE. _Oenothera_s are native to America and all of the species growing in Europe have escaped from gardens directly, or may have arisen by mutation, or by hybridization of introduced species. A fixed hybrid between _O. cruciata_ and _O. biennis_ constituting a species has been in cultivation for many years. The form known as _O. biennis_ in Europe, and used by de Vries in all of the experiments described in these lectures, has not yet been found growing wild in America and is not identical with the species bearing that name among American botanists. Concerning this matter Professor de Vries writes under date of Sept. 12, 1905: "The '_biennis_' which I collected in America has proved to be a motley collection of forms, which at that time I had no means of distinguishing. No one of them, so far as they are now growing in my garden is identical with our _biennis_ of the sand dunes." The same appears to be the case with _O. muricata_. Plants from the Northeastern American seaboard, identifiable with the species do not entirely agree with those raised from seed received from Holland. _O. lamarckiana_ has not been found growing wild in America in recent years although the evidence at hand seems to favor the conclusion that it was seen and collected in the southern states in the last century. (See MacDougal, Vail, Shull, and Small: Mutants and Hybrids of the _Oenotheras_. Publication 24. Carnegie Institution. Washington, D.C., 1905.) EDITOR. [576] LECTURE XX THE ORIGIN OF WILD SPECIES AND VARIETIES New species and varieties occur from time to time in the wild state. Setting aside all theoretical conceptions as to the common origin of species at large, the undoubted fact remains that new forms are sometimes met with. In the case of the peloric toad-flax the mutations are so numerous that they seem to be quite regular. The production of new species of evening-primroses was observed on the field and afterwards duplicated in the garden. There is no reason to think that these cases are isolated instances. Quite on the contrary they seem to be the prototypes of repeated occurrences in nature. If this conception is granted, the question at once arises, how are we to deal with analogous cases, when fortune offers them, and what can we expect to learn from them?