While the polyphyletic origin of species is in a fair way to be decided by experiment, it receives support from several well-known phenomena. The striking similarity in the plant body of families taxonomically so distinct as the _Cactaceae_, _Stapeliaceae_, and _Euphorbiaceae_, or _Cyperaceae_ and _Juncaceae_, indicates that a vegetation form may be polyphyletic. On the other hand, the local appearance of zygomorphy, of symphysis, and of aphanisis in the floral types of phylogeneticallv distinct families is a proof of the operation of convergence in reproductive characters. To be sure, the convergence is never so great as to produce more than superficial similarity, but this is because the groups are markedly different in so many fundamental characters. The same tendency in closely related species would easily result in identity. As in the case of polygenesis, the relatively small number of typically distinct habitats makes it clear that two different species of wide distribution, bearing to each other the relations of xerophyte to mesophyte, of hydrophyte to mesophyte, or of poophyte to hylophyte, might often find themselves in reciprocal situations, with the result that they would give rise to the same new form. The final proof of the polyphylesis of species is afforded by the experiments of De Vries in mutation. De Vries found that _Oenothera nanella_ arose from _O. Lamarckiana_, _O. laevifolia_, and _O. scintillans_; _Oenothera scintillans_ arose from _O. lata_ and _O. Lamarckiana_; _Oenothera rubrinervis_ from _O. Lamarckiana_, _O. laevifolia_, _O. lata_, _O. oblonga_, _O. nanella_, and _O. scintillans_, etc. Whatever may be the rank assigned to these mutations, whether form, variety, or species, there can be no question of their polyphyletic origin, nor, in consequence of the connection of mutations with variations through such inconstant forms as _O. scintillans_, _O. elliptica_, and _O. sublinearis_, of the possibility of polyphylesis in any two distinct though related species or genera. _KINDS OF INVASION_