APPENDIX. 599 



goes to press, and in it the benefit of cross-fertilisation is fairly proved so 

 far as cultivated plants are concerned. ' ; Self- fertilisation assures the pro- 

 duction of a large supply of seeds ; cross-fertilisation, however, not only 

 does this in a more thorough manner, but the plants from cross -fertilised 

 seeds are much more vigorous, and their seedlings more fertile and more 

 variable, than self- fertilised seedlings. The greatest good follows cross- 

 fertilisation when one of the parents has been grown under different condi- 

 tions, by which its characters have been altered or differentiated, or if one 

 has varied spontaneously (or 'sported'), the results are generally good. 

 If injury ever does follow self-fertilisation, it is owing to the want of varia- 

 tion or mutual attraction in the sexual elements." If fixity or permanence 

 is requisite in any particular variety, the best way to obtain this is to care- 

 fully self-fertilise the plant so as to keep its distinctive characters pure ; and 

 if this is done for six or seven generations, the result is that seeds from 

 plants so treated reproduce the form with tolerable exactness. Cultivators 

 have long known the advantages of change of seed, and Mr Gower* had 

 pointed out the advantages of cross-fertilisation with a different individual 

 from a fresh stock in 1869 ; but Mr Darwin's last contribution to science 

 is of immense importance, as proving this in a more satisfactory manner. 

 We have now abundant evidence that a larger productiveness in the way of 

 flowers, fruits, and fertile seeds follows judicious cross-fertilisation than 

 where no interference in that way has been instituted ; indeed, most striking 

 evidence of the beneficial results obtainable by the blending or cross-breed- 

 ing of races is afforded by the Old Briton, Roman, Saxon, and Norman 

 races now amalgamated under the name of Englishmen. Hybrid and cross- 

 bred seedlings often show evidence of greater fertility and a more vigorous 

 habit of growth than either parent, although this vigour is sometimes ob- 

 tained at the expense of complete or partial sterility. It was formerly 

 thought that all hybrid plants were infertile; but we now find that very few 

 hybrids of the first generation are completely sterile M. Naudin thinks not 

 more than 25 per cent ; while the cross-bred or cultivated varieties of hybrids, 

 as well as those of wild species, are not unfrequently more fertile than 

 either the parent species or the primitive type. Hybrids of hermaphrodite 

 plants may be incapable of bearing fertile seeds under any circumstances, 

 and yet their pollen may be capable of fecundating the ovules of another 

 species or hybrid, as in the case of Nymphaea, Narcissus, and Passiflora ; 

 while on the other hand, some hybrids (as well as wild species) have im- 

 potent pollen, but are readily rendered fertile by the application of pollen 

 from an allied species or variety. As it is possible for either the male or 

 female organs of a hermaphrodite plant to become impotent through the 

 disturbing influence of high culture, hybridism, or cross-fertilisation, so also 

 is it not uncommon for monoecious plants Begonias, for example to be- 

 come hermaphrodite ; and dioecious plants, as Coelebogyne, Aucuba, and 

 Skimmia, sometimes bear anthers among the female organs of flowers on 

 the female plants ; while, as has been shown by Spruce and others, it is not 

 unusual for dioecious Palms and other plants suddenly to produce male 

 instead of female flowers, or vice versd. Mr Meehan and other observers 

 have pointed out that nutrition influences the production or strength of the 

 sexual organs more than is generally supposed, and of this we get some 

 evidence in the case of trees grafted on restricting stocks, which are thus 

 rendered more fruitful ; and we know that a course of semi-starvation leads 

 to fruitfulness as a rule, just as over-feeding leads to vegetative growth 

 and leafy exuberance ; and even the alternate production of male and 

 female flowers on dioecious plants may be due to external conditions. 



* Williams's Choice Stove and Greenhouse Flowering-Plants, p. 31. 



