Chap. XVII. EVIL FROM INTERBREEDING. Ill 



Here is a remarkable case : M. Clotzsck 57 crossed Pinus sylvestris 

 and nigricans, Quercus robur and ptduncidata, Alnus glutinosa and 

 incana, Ulmus campestris and effusa ; 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 botanists 

 as strongly-marked 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 58 

 sums up his conviction on this head in the strongest terms. Kol- 

 reuter 69 gives numerous precise measurements of the weight and 

 height of his hybrids in his comparison with measurements of both 

 parent-forms ; and speaks with astonishment of their stutura por- 

 " tentosa," their "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 Herbert; but the most 

 striking exceptions are given by Max Wichura, 60 who found that 

 hybrid willows were generally tender in constitution, dwarf, and 

 short-lived. 



Kolreuter explains the vast increase in the size of the roots, 

 stems, &c, of his hybrids, as the result 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; 61 

 but Gartner 62 has well remarked that there is much difficulty in 

 fully admitting it ; for with 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 



5 ' Quoted in ' Bull. Bot. Soc. 6 ° ' Die Bastardbefruchtung,' &c, 



France,' toL ii., 1855, p. 327. 1865, s. 31, 41, 42. 



58 Gartner, ' Bastarderzeugung,' s. 61 Max Wichura fully accepts this 

 259, 518, 526 et seq. view (' Bastardbefruchtung,' s. 43), 



59 ' Fortsetzung,' 1763, s. 29; as does the Rev. M.J. Berkeley, in 

 ' Dritte Fortsetzung,' s. 44, 96 ; 'Act. 'Journal of Hort. Soc.,' Jan. 1866, 

 Acad. St. Petersburg,' 1782, part ii., p. 70. 



p. 251; 'Nova Acta,' 1793, pp. 391, 62 'Bastarderzeugung,' s. 394, 526, 



394; 'Nova Acta,' 1795, pp. 316, 528. 



323. 



