Some flowers of the _Mimulus luteus_ were fertilised with their own pollen, and others were crossed with pollen from distinct plants growing in the same pot. The seeds after germinating were thickly planted on opposite sides of a pot. The seedlings were at first equal in height; but when the young crossed plants were exactly half an inch, the {129} self-fertilised plants were only a quarter of an inch high. But this inequality did not continue, for, when the crossed plants were four and a half inches high, the self-fertilised were three inches; and they retained the same relative difference till their growth was complete. The crossed plants looked far more vigorous than the uncrossed, and flowered before them; they produced also a far greater number of flowers, which yielded capsules (judging, however, from only a few) containing more seeds. As in the former case, the experiment was repeated in the same manner during the next two generations, and with exactly the same result. Had I not watched these plants of the Mimulus and Ipomoea during their whole growth, I could not have believed it possible, that a difference apparently so slight, as that of the pollen being taken from the same flower, and from a distinct plant growing in the same small pot, could have made so wonderful a difference in the growth and vigour of the plants thus produced. This, under a physiological point of view, is a most remarkable phenomenon. * * * * * With respect to the benefit derived from crossing distinct varieties, plenty of evidence has been published. Sageret[287] repeatedly speaks in strong terms of the vigour of melons raised by crossing different varieties, and adds that they are more easily fertilised than common melons, and produce numerous good seed. Here follows the evidence of an English gardener:[288] "I have this summer met with better success in my cultivation of melons, in an unprotected state, from the seeds of hybrids (_i.e._ mongrels) obtained by cross impregnation, than with old varieties. The offspring of three different hybridisations (one more especially, of which the parents were the two most dissimilar varieties I could select) each yielded more ample and finer produce than any one of between twenty and thirty established varieties." Andrew Knight[289] believed that his seedlings from crossed varieties of the apple exhibited increased vigour and luxuriance; and M. Chevreul[290] alludes to the extreme vigour of some of the crossed fruit-trees raised by Sageret.