Cross- and Self -Fertilization 29 



however, one desires to impart single definite qualities to 

 one variety and he derives these from another variety, 

 sometimes even from another species. Hardening against 

 winter-frost has frequently been transmitted in this man- 

 ner from one form to another. Carriere 15 cites instances of 

 Begonias which, through crossing with a variety of an- 

 other species with variegated leaves, have been made 

 varigated without having their other qualities changed. 

 The conviction is really quite general in horticultural 

 practice that, by crossings, one may combine the charac- 

 ters of varieties at will, and thus improve his races ac- 

 cording to his needs in many as well as in individual 

 desirable points. 



6. Cross- and Self-fertilisation 

 In addition to the arguments dealt with in the pre- 

 ceding paragraph, which gives us the results of ex- 

 periments in crossing and hybridization, we will now 

 consider normal fertilization and see to what extent, in 

 this domain, the facts support our conception of the mu- 

 tual independence and miscibility of hereditary charac- 

 ters. 



To fathom the meaning of fertilization is one of the 

 most difficult problems of biology. The numerous adapta- 

 tions of this process to the most varied conditions of life, 

 and the powerful influence which it has exercised on the 

 differentiation of species, especially through the develop- 

 ment of the secondary sexual characters, threaten always 

 to mislead us, and to make us mistake its essential nature 

 through its later acquired significance. Here, as in so 

 many cases, the conditions in the plant kingdom are clearer 



15 Carriere, E. A. Production et fixation des varietes, p. 22. 1865. 

 Other examples are given by Verlot, Sur la production et la fixation 

 des varietes. pp. 46 and 65. 1865. Cf. also Darwin, loc. cit. 2: 73. 



