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Show 128 GOOD FROM CROSSING. CHAP. XVII. reverse d case. Tho Solf-£ortilisod and crossed seeds thus obtained wore al l owocl t o gcrmi·l l,n. te 1·n tJ1e sa" me glass vessel on dam. p sa.n d; and as th. o seeds snccossivoly germinated, they were planted ill pan·s on opposite sides of the same pot, with a superficial partition between them, and were placed so as to be equally exposed to the light. In othm: cas~s the selffertilised and crossed seeds were ::;imply so~n on opposite side~ of tho same small pot. I have, in short, followed different p~ans, but m every case have taken all tho precautions which I could thillk of, so that tho t lots should be equally favomed. Now, I have carefully observed t~~ growth of plants raised from crossed and self-f~rtilisod seed, from their germination to matmity, in sp?cios of the fo~owmg genera, n~moly, Brassica, Lathyrus, Lupinus, Lobelia, Laduca, Dianthus, M~osot1s, P?tunia, Linaria, Calcoolaria, Mimulus, an~ Ip?mooa, ~nd tho difference m their powers of growth, and of withstanding ill cm·taill ca~es u~favourablo conditions, was most manifest and strongly marked. It 1s of ~po_rtanco that the two lots of seed should be sown qr planted on oppos1to sides of the same pot, so that tho seedlings may struggle against eac~ othe:·; for if sown separately in ample and good soil, there is often but httle difference in their growth. · I will briefly describe the two most striking cases as yet observed by me. Six crossed and six self-fertilised seeds of Ij_wmrea purpurea, from plants treated in tho manner above described, wore planted as soon as they had germinated, in pairs on opposite sides of two pots, and rods of equal thickness were given them to twine up. Five of the crossed plants grow from the fu·st more quicldy than tho opposed self-fertilised plants; tho sixth, however, was weakly and was for a time beaten, but at last its sounder constitution prevailed and it shot ahead of its antagonist. As soon as each crossed plant reached the top of its seven-foot rod its follow was mcasmod, and tho result was that, when tho crossed plants were seven foot high, the self-fertilised had attained the average height of only five feet four and a half inches. The crossed plants flowered a little before, and more profusely than the self-fertilised plants. On opposite sides of another small pot a largo number of crossed and self-fertilised seeds were sown, so that they had to struggle for bare existence ; a single rod was given to each lot : hero again tho crossed plants showed from the first their advantage; they never quite reached the summit of the seven-foot rod, but relatively to tho self-fertilised plants their average height was: as seven feet to five feet two inches. The experiment was repeated in the two following generations with plants raised from the self-fertilised and crossed plants, treated in exactly tho same manner, and with nearly the same result. In the second generation, the crossed plants, which were again crossed, produced 121 seed-capsules, whilst the self-fertilised plants, again self-fertilised, produced only 84 capsules. 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 fu·st equal in height; but when the young crossed plants were exactly half an inch, the self- CuAP. XVII. EVIL FROM INTERBREEDING. 129 fertilised plants were only a quarter of an inch high. But this inequality did I 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 fa:~; 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 Ipomcea 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 43 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: 44 "I have this summer met with better success in my culti" vation 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." And.I·ew Knight 4.s believed that his seedlings from crossed varieties of the apple exhibited increased vigour and luxuriance; and M. Chevreul 46 alludes to the extreme vigour of some of the crossed fruit-trees raised by Sageret. By crossing reciprocally the tallest and shortest peas, Knight 47 says, " I had in this experiment a striking instance of the stimulative effects "of crossing the breeds; for the smallest variety, whose height rarely " exceeded two feet, was increased to six feet; whilst the height of the "large and luxuriant kind was very little diminished." Mr. Laxton gave me seed-peas produced from crosses between four distinct kinds; and the plants thus raised were extraordinarily vigorous, being in each case from one to two or three feet taller than the parent-forms growing close alongside them. 43 ' Memo ire sur les Cucurbit.acees,' pp. 36, 28, 30. • 44 Loudon's 'Gard. Mag.,' vol. viii., 1832, p. 52. 45 'Transact. Hort. Soc.,' vol. i. p. 25. VOL. II. 46 'Annal. des Sc. Nat.,' 3rd series, llot., tom. vi. p. 189. 47 'Philosophical Transactions,' 1799, p. 200. K |