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The Journal of the Linnæan Society, No. 31 (Dec. 1864), is especially rich in articles upon Dimorphism and even Trimorphism in plants, and upon the agency of insects in their fertilization. […]

5. On the Sexual Relations of the three forms of Lythrum Salicaria, by Charles Darwin. Here we have the results of an investigation which Mr. Darwin has before

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referred to. A curious case it is, and treated with the wonted sagacity and point of this prince of biological inquirers.

"In Lythrum Salicaria three plainly different forms occur: each of these is an hermaphrodite; each is distinct in its female organs from the other two forms; and each is furnished with two sets of stamens or males, differing from each other in appearance and function. Altogether, there are three females and three sets of males, all as distinct from each other as if they belonged to different species; and, if smaller functional differences are considered, there are five distinct sets of males. Two of the three hermaphrodites must co-exist, and the pollen be carried by insects reciprocally from one to the other, in order that either of the two should be fully fertile: but, unless all three forms co-exist, there will be waste of two sets of stamens, and the organization of the species as a whole will be imperfect. On the other hand, when all three hermaphrodites co-exist, and the pollen is carried from the one to the other, the scheme is perfect; there is no waste of pollen and no false co-adaptation. In short, Nature has ordained a most complex marriage-arrangement, namely, a triple union between three hermaphrodites, each hermaphrodite being in its female organ quite distinct from the other two hermaphrodites, and partially distinct in its male organs, and each furnished with two sets of males."

One must study this instructive paper to see how neatly it is shown, "that only the longest stamens fully fertilize the longest pistil, the middle stamens the middle pistil, and the shortest stamens the shortest pistil. And now we can comprehend the meaning of the almost exact correspondence in length between the pistil of each form and the two half- dozen sets of stamens borne by the two other forms; for the stigma of each form is thus rubbed against the same spot of the insect's body which becomes most charged with the proper pollen." For the use which Mr. Darwin makes of this case, and the theoretical deductions drawn from a genus which presents trimorphic, dimorphic, and monomorphic species, the illustration of the advantage of trimorphism, and of the now established fact that sexual differences,—"thought to be the very touchstone of specific distinction,"—may characterise and keep separate the coexisting individuals of the same species in the same manner as they do those groups of individuals which we denominate species, we must refer to the memoir itself, not having space for a full abstract. Mr. Darwin, on raising from seed some individuals of our Nesæa verticillata, ascertained that this plant is also trimorphic. We commend it to the particular attention of any who may be disposed to prosecute farther such investigations, which, though requiring genius to originate, are easy to follow up, and almost inexhaustible in interest.