It seems to me that in these facts, established by observation, the results of two quite different processes have been confused, and that we can only gain clearness by studying them apart from one another; I mean the processes involved in the mechanism of fertilization and those involved in the mingling of the germ-plasms. In many cases self-fertilization is said to yield less seed and weaker seedlings. Let us for the present take this statement as the basis of our consideration; it does not seem to me conceivable, though here I am not in agreement with views that have been expressed by others, that both effects should depend upon the same causes, for the smaller number of seeds cannot possibly depend upon the mingling of the two parental germ-plasms, and thus not upon the process of amphimixis itself, since the effect of the mingling does not make itself felt until the organism of the offspring is being built up. Of course the plant seed is the embryo of the young plant, but it will hardly be thought probable that its development could be absolutely prevented by the too close relationship of the two germ-cells, and thus the number of the developing seeds cannot depend on the quality of the ids co-operating in the segmentation-nucleus, but presumably on the number of ova awaiting fertilization in the ovary, which are reached by a pollen-tube and then by a paternal sex-nucleus. This again will depend upon the impelling and attracting forces of the pollen-grain on the one hand, and of the stigma and 'embryo-sac' of the flower on the other. In other words, the fertility of a flower with its own pollen will depend upon whether the two products of the flower are adapted for mutual co-operation, and in what degree they are so. We are here dealing not with the _primary_ reactions of the germ-plasms, which are as they are and cannot be varied, but with secondary relations, which may be thus or thus--in short, with _adaptations_.