all give a mixture of two distinct types which he names laeta and velutina, consisting of about equal numbers of each. On account of the fact that the two forms are produced in association de Vries has called these forms "twin hybrids," a designation which is not fortunate, seeing that it is impossible to imagine that any kind of twinning is concerned in their production. The distinction between these two seems to be considerable, laeta having leaves broader, bright green in colour, and flat, with pollen scanty, while velutina has leaves narrower, grayish green, more hairy, and furrow-shaped, with pollen abundant.
We next meet the remarkable fact that these two forms, laeta and velutina breed true to their respective types, and do not reproduce the parent-types among their offspring resulting from self-fertilisation. This statement must be qualified in two respects. When muricata ♂ is fertilised by brevistylis the forms laeta and velutina are produced, but each of them subsequently throws the short-styled form as a recessive (de Vries, 1907, p. 406). It may be remembered that de Vries's previous publications had already shown that the short style of brevistylis, one of the Lamarckiana "mutants," behaves as a recessive habitually (Mutationstheorie, II, p. 178, etc.).
Also when nanella, the dwarf "mutant" of Lamarckiana is used as male on muricata as female, laeta and velutina are produced, but one only of these, namely, velutina, subsequently throws dwarfs on self-fertilisation. The dwarfs thus thrown are said to form about 50 per cent. of the families in which they occur (de Vries, 1908, p. 668). The fact that the two forms, laeta and velutina, are produced by many matings in which Lamarckiana and its mutant rubrinervis are used as males is confirmed abundantly by Honing, who has carried out extensive researches on the subject. After carefully reading his paper, I have failed to understand the main purport of the argument respecting the "double nature" of Lamarckiana which he founds on these results, but I gather that in some way laeta is shown to partake especially of the nature of Lamarckiana, while velutina is a form of rubrinervis. The paper contains many records which will be of value in subsequent analysis of these forms.
Before considering the possible meaning of these facts we must have in our minds the next and most novel of the recent extensions of knowledge as to the genetic properties of the Oenotheras. In the previous statement we have been concerned with the results of using either Lamarckiana itself or one of its "mutants" rubrinervis, brevistylis, or nanella as male, on one of the species biennis or muricata. The new experiments relate to crosses between the two species biennis and muricata themselves.
De Vries found:
1. That the reciprocal hybrids from these two species differed, biennis × muricata producing one type of F1 and muricata × biennis producing another. Each F1 resembled the father more than the mother.
2. That each of the hybrids so produced breeds true on self-fertilisation.
3. That if we speak of the hybrid from biennis × muricata as BM and of the reciprocal as MB, then
BM × MB
gives exclusively offspring of biennis type but that