Heterostylous plants may possibly be the means of establishing my view that the law of sexual complements holds good for every kind of living thing. Darwin first, and after him many other investigators have proved that in heterostylous plants fertilisation has the best results, or, indeed, may be possible only when the pollen from a macrostylous flower (a flower with the shortest form of anthers and longest pistil) falls on the stigma of a microstylous blossom (one where the pistil is the shortest possible and the stamens at their greatest length), or _vice versâ_. In other words, if the best result is to be attained by the cross-fertilisation of a pair of flowers, one flower with a long pistil, and therefore high degree of femaleness, and short stamens must be mated with another possessing a correspondingly short pistil, and so, with the amount of femaleness complementary to the first flower, and with long stamens complementary to the short stamens of the first flower. In the case of flowers where there are three pistil lengths, the best results may be expected when the pollen of one blossom is transmitted to another blossom in which the stigma is the nearest complement of the stigma of the flower from which the pollen came; if another combination is made, either naturally or by artificial fertilisation, then, if a result follows at all, the seedlings are scanty, dwarfed and sometimes infertile, much as when hybrids between species are formed. It is to be noticed that the authors who have discussed heterostylism are not satisfied with the usual explanation, which is that the insects which visit the flowers carry the pollen at different relative positions on their bodies corresponding to the different lengths of the sexual organs and so produce the wonderful result. Darwin, moreover, admits that bees carry all sorts of pollen on every part of their bodies; so that it has still to be made clear how the female organs dusted with two or three kinds of pollen make their choice of the most suitable. The supposition of a power of choice, however interesting and wonderful it is, does not account for the bad results which follow artificial dusting with the wrong kind of pollen (so-called “illegitimate fertilisation”). The theory that the stigmas can only make use of, or are capable of receiving only “legitimate pollen” has been proved by Darwin to be erroneous, inasmuch as the insects which act as fertilisers certainly sometimes start various cross-breedings.