The characters borne by the male parts of the two species are in general those by which they are outwardly distinguished. For example, the leaves of _Oe. biennis_ are comparatively broad and are bright green, while those of _muricata_ are much narrower and of a glaucous green, and I understand that de Vries regards these properties as contributed by the male side in each case and to be carried by the male cells of each species. The suggestion as regards _biennis_ and _muricata_ comes near the conception often expressed by naturalists in former times (_e. g._, Linnaeus) and not rarely entertained by breeders at the present day, that the internal structure is contributed by the mother and the external by the father. On the other hand, the offspring of each species when used as mother is regarded as possessing in the main the features of the maternal "Bild," but the matter is naturally complicated by the introduction of features from the father's side, and it is here especially that the account provided is at present unsatisfactory and inconclusive. There seems, however, to be no serious doubt that _biennis_ and _muricata_ each in their outward appearance exhibit on the whole the features which their pollens respectively carry, and that the features borne by their ovules are in many respects distinct. The _types_ are thus "hybrids" which breed true. The results of intercrossing them each way are again "hybrids" which breed true. It will be remembered that on former occasions de Vries has formulated a general rule that _species_-hybrids breed true, but that the cross-breds raised by interbreeding _varieties_ do not. One of these very cases was quoted[7] as an illustration of this principle, viz: _muricata_ × _biennis_. The grounds for this general statement have always appeared to me insufficient, and with the further knowledge which the new evidence provides we are encouraged to hope that when a proper factorial analysis of the types is instituted we shall find that the phenomenon of a constant hybrid will be readily brought into line with the systems of descent already worked out for such cases as that of the Stocks, and others already mentioned.