The Knight-Darwin Law1


THE law under the above title is known to botanists through H. Müller (“Befruchtung der Blumen,” Eng. trans., p. 4), who says that Andrew Knight “laid down the law that in no plant does self-fertilisation occur for an unlimited number of generations.” This he call's Knight's Law, and later, in sub stantially the same form, it becomes the Knight-Darwin Law. For the statement of Knight's Law the reader is referred to that author's celebrated paper: “An account of some experiments on the fecundation of vegetables”(Phil. Trans., 1799). The words, however, do not occur in Knight's paper, and I imagine that Müller got them from Charles Darwin's paper on the fertilisation of papilionaceous flowers, where occurs the passage (Gardener's Chronicle, 1858): “Andrew Knight many years ago propounded the doctrine that no plant self-fertilises itself for a perpetuity of generations.”2 The words are not given in inverted commas, and I strongly suspect that, with a singular lapse of his usual accuracy, my father was merely giving his own interpret ation of the conclusion which seemed to flow from Knight's expressions when taken with the whole of the context. For in the “Effects of Cross- and Self-fertilisation,” 1876, p. 7, he quotes Knight's actual words. After referring to Sprengel, he goes on: “Andrew Knight saw the truth much more clearly, for he remarks: ‘; Nature intended that a sexual intercourse should take place between neighbouring plants of the same species’…” and again: “‘Nature has something more in view than that its own proper males should fecundate each blossom.’” Here we have simply the general statement that hermaphrodite flowers are not necessarily self-fertilised; a statement of fundamental import ance in floral biology. If the positive statement that “no plant self-fertilises itself for a perpetuity of generations” is to be found elsewhere in Knight's writings, I think Darwin would have quoted it.


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DARWIN, F. The Knight-Darwin Law1. Nature 58, 630–632 (1898).

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