and thus there is an asymmetrical curve of frequency. But if we take the whole area of variation as the area of exemption, that is, if we assume that it is indifferent for the species whether the flowers have five, six, seven, or eight petals, the preponderance of the five-petalled flowers may have its reason in the fact that it is much easier for five than six or more petals to be produced because of the internal structure of the whole plant. In this case the maximum of frequency lies at the lower limit of variation, but it may also lie at the upper. Thus, according to De Vries, the blossoms of _Weigelia_ vary, in regard to the number of their petal-tips, in the following manner. Six-tipped corollas were not found, and among 1,145 flowers there were the following proportions:-- Tips of the corolla 3 4 5 Number of flowers 61 196 888 It is thus clear that amphimixis is an essential factor in the fixing of forms, but that it certainly does not of itself determine these, and that it is not always the average of the variations that is the most frequent, but that the form of the curve of frequency is determined by other factors also, namely, by germinal and personal selection and by the directive control which these exert on variations. The equalizing effect of amphigony may perhaps be expressed thus: In the case of every new adaptation there is at first a large area of variation, but this gradually decreases owing to a continual restriction on the part of natural selection, until ultimately--when the highest degree of constancy of the character or species has been attained--it only extends very little beyond the 'adaptation-playground' or the 'area of exemption.' One of the effects of amphimixis is thus to bring about an increasing restriction of the area of variation, or, as we usually say, a constancy of the facies of a given form, a condensation into a species. How far this result is necessary or useful, and therefore how far it may be regarded as accounting for the persistence of amphimixis, we shall discuss in the chapter on the formation of species. My own view is that even the fact that new adaptations are rendered possible through amphimixis and amphigony, the mode of reproduction associated with it, affords in itself a sufficient reason why amphimixis should have been retained when once it had been introduced. LECTURE XXIX THE GENERAL SIGNIFICANCE OF AMPHIMIXIS (_continued_)