Now it must be granted that the energizing of such a propensity under ordinary circumstances is quite another thing from the origination of a positive variety by the evolution of the same character. In the variety the activity has become independent of outer influences or dependent upon them in a far lesser degree. The power of producing the red pigments is shown to be latent by the facts given above, and we see that in the variety it is no longer latent but is in perfect and lasting activity throughout the whole life of the plant. Red varieties of white flowers are much more rare. Here the latency of the red pigment may be deduced partly from general arguments like those just given, partly from the special systematic relations in the given cases. Hildebrand has clearly worked out this mode of proof. He showed by the critical examination of a large number of instances that the occurrence of the red-flowered varieties is contingent upon the [241] existence of red species in the same genus, or in some rare cases, in nearly allied genera. Colors that are not systematically present in the group to which a white species belongs are only produced in its varieties in extremely rare cases. We may quote some special rules, indicated by Hildebrand. Blue species are n the main very rare, and so are blue varieties of white species also. Carnations, Asiatic or cultivated buttercups (_Ranunculus asiaticus_), _Mirabilis_, poppies, _Gladiolus_, _Dahlia_, and some other highly cultivated or very old garden-plants have not been able to produce true blue flowers. But the garden-anemone (_Anemone coronaria_) has allies with very fine blue flowers. The common stock has bluish varieties and is allied to _Aubretia_ and _Hesperis_, and gooseberries have a red form, recalling the ordinary currant. In nearly all other instances of blue or red varieties every botanist will be able to point out some allied red or blue species, as an indication of the probable source of the varietal character. Dark spots on the lower parts of the petals of some plants afford another instance, as in poppies and in the allied _Glaucium_, where they sometimes occur as varietal and in other cases as specific marks. The yellow fails in many highly developed [242] flowers, which are not liable to produce yellow variations, as in _Salvia_, _Aster_, _Centaurea_, _Vinca_, _Polygala_ and many others. Even the rare pale yellowish species of some of these genera have no tendency in this direction. The hyacinths are the most remarkable, if not the sole known instance of a species having red and blue and white and yellow varieties, but here the yellow is not the bright golden color of the buttercups. The existence of varietal colors in allied species obviously points to a common cause, and this cause can be no other than the latency of the pigment in the species that do not show it.