Chap. XVII. 



EVIL FROM INTERBREEDING. 



131 



Herbert ; but the most striking exceptions are given by Max Wichura, 54 

 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 ; 55 but Gartner 56 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 extra- 

 ordinary luxuriance of growth, together with their enormous roots, 57 have 

 been transmitted to their progeny. The increased size of the hybrids pro- 

 duced between the fowl and pheasant, and between distinct species of phea- 

 sants, has been already noticed. The result in all cases is probably in part 

 due to the saving of nutriment and vital force through 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 vigour 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 

 accounts for it by the pollen of the hybrid, and probably its ovules, being 

 in some degree vitiated, whereas the pollen and ovules of both pure 

 parents and of any third species are sound. Nevertheless 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 of hybrids. 



On certain Hermaphrodite Plants which, either normally or abnor- 

 mally, 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 Max Wichura fully accepts this 

 view (' Bastardbefruchtung,' s. 43) as 

 does the Rev. M. J. Berkeley, in ' Jour- 

 nal of Hort. Soc./ Jan. 1866, p. 70. 



5G 'Bastarderzeugung,' s. 394, 526, 

 528. 



57 Kolreuter, 'Nova Acta,' 1795, p. 

 316. 



58 Gartner, 'Bastarderzeugung,' s. 

 430. 



K 2 



