2^0 Heredity, 



that variation is much more marked and common in 

 plants raised from fertilized seed than in those raised by 

 budding. A marked bud-variation is a very rare occur- 

 rence, but in many cases the tendency of plants reared 

 from seeds to diifer from the parents is so great that 

 choice varieties are propagated entirely by buds. It is 

 almost hopeless to attempt to propagate a choice variety 

 of grape or strawberry by seeds, as the individuals reared 

 in this way seldom have the valuable qualities of their 

 parents, and, although they may have new qualities of 

 equal or greater value, the chances are of course greatly 

 against this, since the possibility of undesirable varia- 

 tion is much greater than the chance of a desirable sport. 

 There is no difficulty, however, in })erj)etuating valuable 

 varieties of these plants by asexual reproduction. 



Putting together these various propositions — that the 

 evolution of life has been brought about through the 

 combined action of the law of heredity and the law of 

 variation; that in all except the simplest organisms the 

 process of sexual reproduction by ova which have been 

 acted upon by the male element is met with; that the 

 ovum is alive, and capable of development in itself, and 

 that the essential function of the male element is some- 

 thing else than the vitalization of the ovum; that the 

 process of sexual reproduction differs from the process 

 of asexual reproduction only in the occurrence of im- 

 pregnation, while the result of the former process differs 

 from the result of the latter in its greater variability — 

 we seem warranted in concluding that the ovum is the 

 material medium through which the law of heredity 

 manifests itself, while the male element is the vehicle 

 by which new variations are added. The ovum is the 

 conservative and the male element the progressive or 

 variable factor in the process of evolution of the race as 



