The heterostyled trimorphic plants, of which _Lythrum salicaria_, Figure 5 C, D, E, may be taken as an example, are even more remarkable. There are three different kinds of flowers: in one the pistil is long and there is a medium and a short set of stamens; in another the pistil is of intermediate length and there is a long set and a short set of stamens; in the third kind the pistil is short, and there is a medium and a long set of stamens. There are possible only six sorts of legitimate unions between these three sets of flowers. No less than twelve kinds of illegitimate unions may occur. In regard to the difference in the sizes of the pollen grains, those from the long-styled form are the largest, from the mid-styled form next, and from the short-styled form the smallest. The extreme difference is as 100 to 60. “Nothing shows more clearly the extraordinary complexity of the reproductive system of this plant than the necessity of making eighteen distinct unions in order to ascertain the relative fertilizing power of the three forms.” Darwin tried the effect of each of these combinations, making 223 unions in all. The results are surprising. Comparing the outcome of the six legitimate unions with the twelve illegitimate ones, the following results were obtained:— ═══════════════╤══════════╤══════════╤══════════╤══════════ │Number of │ │ │ Average │ Flowers │Number of │ Average │ No. of Nature of Union│Fertilized│ Capsules │ No. of │Seeds per │ │ Produced │Seeds per │ Flower │ │ │ Capsule │Fertilized ───────────────┼──────────┼──────────┼──────────┼────────── The 6 │ 75 │ 56 │ 96.29 │ 71.89 legitimate │ │ │ │ unions │ │ │ │ ───────────────┼──────────┼──────────┼──────────┼────────── The 12 │ 146 │ 36 │ 44.72 │ 11.03 illegitimate │ │ │ │ unions │ │ │ │ ═══════════════╧══════════╧══════════╧══════════╧══════════ This table shows that the fertility of the legitimate to that of the illegitimate is as 100 to 33, as judged by the flowers that produced capsules; and as 100 to 46 as judged by the average number of seeds per capsule. It is evident, therefore, that “it is only the pollen from the longest stamens that can fully fertilize the longest pistil; only that from the mid-length stamens, the mid-length pistil; and only that from the shortest stamens, the shortest pistil.”