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Show 130 GOOD FROM CROSSING. CnAP. XVIf. Wiegmann 48 made many crosses between several varieties of cabbage; and he speaks with astonishment of the vigour and height of the mongrels, which excited the amazement of all the gardeners who beheld them. Mr. Chaundy raised a great number of mongrels by planting together six distinct varieties of cabbage. These mongrels displayed an infinite diversity of character; "But the most remarkable circumstance was, "that, while all the other cabbages and borecoles in the nursery were "destroyed by a severe winter, these hybrids were little inj:tll'ed, and "supplied the kitchen when there was no other cabbage to be had." Mr. Maund exhibited before the Royal AgTicultural Society 49 specimens of cmssed wheat, together with theiT parent varieties; and the editor states that they were intermediate in character, "united with that greater vigour of growth, which it appears, in the vegetable as in the animal world, is the result of a first cross." Knight also crossed several varieties of wheat ,5° and he says " that in the years 1795 and 1796, when almost " the whole crop of corn in the island was blighted, the varieties thus "obtained, and these only, escaped in this neighbourhood, though sown "in several different soils and situations." Here is a remarkable case : M. Clotzsch 51 crossed Pinus sylvestris and nigricans, Quercus robur and pedunculata, Alnus ghttinosa and incana., Dlmus campest1·is and etfusa; and the cross-fertilised seeds, as well as seeds of the pure parent-trees, were all sown at the same time and in the· same place. The result was, that after an interval of eight years, the hybrids were one-third taller than the pure trees ! The facts above given refer to undoubted varieties, excepting the trees crossed by Clotzsch, which are ranked by various botanist~ · as stronglymarked races, sub-species, or species. That true hybrids raised from entirely distinct species, though they lose in fertility, often gain in size and constitutional vigour, is certain. It would be superfluous to quote any facts; for all experimenters, Kolreuter, Gartner, Herbert, Sageret, Lecoq, and Naudin, have been struck with the wonderful vigour, height, size, tenacity of life, precocity, and hardiness of their hybrid productions. Gartner 52 sums up his conviction on this head in the strongest terms. Kolreuter 53 gives numerous precise measurements of the weight and height of his hybrids in comparison with measurements of both parent-forms; and speaks with astonishment of their " statura portentosa," theiT " ambitus vastissimus ac altitudo valde conspicua." Some exceptions to the rule in the case of very sterile hybrids have, however, been noticed by Gartner and 48 'Ueber die Bastarderzeugung,' 1828, s. 32, 33. For Mr. Chaundy's case, see Loudon's ' Gard. Mag.,' vol. vii., 1831, p. 696. 49 ' Gardener's Cbron.,' 1846, p. 601. 50 ' Philosoph. Transact. ' 1799 p. 201. ' ' 51 Quoted in 'Bull. Bot. Soc. France,' vol. ii., 1855, p. 327. 52 Gartner, ' Bastarderzeugung,' s. 259, 518, 526 et seq. !3 ' Fortsetztmg,' 1763, s. 29 ; 'Dritte Fortsetzung,' s. 44, 96 ; 'Act. Acad. St. P etersburg,' 1782, part ii., p. 251; 'Nova Acta,' 1793, pp. 391, 394; 'Nova Acta,' 1795, pp. 316, 323. CHAP. XVII. EVIL FROM INTERBREEDING. 131 Herbert; but the most striking exceptions are given by Max Wichura,64 who found that hybrid willows were generally tender in constitution, dwarf, and short-lived. KolTeuter explains the vast increase in the size of the roots, stems, &c., of his hybrids, as the Tesult of a sort of compensation due to their sterility, in the same way as many emasculated animals are larger than the perfect males. This view seems at first sight extremely probable, and has been accepted by various authors; 55 but Gartner 56 has well remarked that there is much difficulty in fully admitting it; for ~th many hybrids there is no parallelism between the degree of their sterility and their increased size and vigour. The most striking instances of luxuriant growth have been observed with hybrids which were not sterile in any extreme degree. In the genus Mirabilis, certain hybrids are unusually fertile, and their extraordinary luxuriance of growth, together with their enormous roots,07 have been transmitted to their progeny. The increased size of the hybrids produced between the fowl and pheasant, and between distinct species ot pheasants, has been already noticed. The result in all cases is probably in part due to the saving of nutriment and vital force thl'Ough the sexual organs not acting, or acting imperfectly, but more especially to the general law of good being derived from a cross. For it deserves especial attention that mongrel animals and plants, which are so far from being sterile that their fertility is often actually augmented, have, as previously shown, their size, hardiness, and constitutional vigour generally increased. It is not a little remarkable that an accession of vigom and size should thus arise under the opposite contingencies of increased and diminished fertility. It is a perfectly well ascertained fact 58 that hybrids will invariably breed more readily with either pure parent, and not rarely with a distinct species, than with each other. Herbert is inclined to explain even this fact by the advantage derived from a cross; but Gartner more justly ~ccounts for it by the pollen of tho hybrid, and probably its ovules, being m some degree vitiated, whereas the pollen and ovules of both pure parents and of any third species are sound. 1'{ evertheless there are some well-ascertained and remarkable facts, which, as we shall immediately see, show that the act of crossing in itself undoubtedly tends to increase or re-establish the fertility ofhybrids. On certain Hermaph1·odite Plants which, either normally or abnormally, require to be fertilised by pollen from a distinct individual or species. The facts now to be given differ from those hitherto detailed, as the self-sterility does not here result from long-continued, 54 ' Die Bastardbefruchtung,' &c., 1865. s. 31, 41, 42. 55 1\fax Wichura fully accepts this view (' Bastardbcfruchtung,' s. 43), as docs the Rev. 1\f. J. Berkeley, in 'Journal of Hort. Soc.,' Jan. 1866, p. 70. 56 ' Bastarderzeugung,' s. 394, 526, 528. 57 Kolreuter, 'Nova Acta,' 1795, p. 316. 68 Gartner, ' Bastarderzeugung,' s. 4:30. I{ 2 |
