iSo THE POPULAR SCIENCE MONTHLY. 



parison can be made without difficulty, and will be found to show that 

 variation is much more marked and common in plants raised from 

 fertilized seed than in those raised by budding. A marked bud-varia- 

 tion is of very rare occurrence, but in many cases the tendency of 

 plants raised from seeds to differ from the parents is so great that 

 choice varieties are propagated entirely by buds. It is almost hope- 

 less to attempt to propagate a choice variety of grape or strawberry 

 by seeds, as the individuals raised in this way seldom have the valua- 

 ble qualities of their parents, and, although they may have new quali- 

 ties of equal or greater value, the chances are of course greatly against 

 this, since the possibility of undesirable variation is much greater than 

 the chance of a desirable sport. There is no difficulty, however, in 

 perpetuating 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 or- 

 ganisms 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 something 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 impregnation, 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 mani- 

 fests itself, while the male element is the vehicle by which new varia- 

 tions 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 well as in the reproduction of the individual. The adequate 

 statement of the evidence upon which this generalization rests, or 

 even a full statement of the generalization itself, with its qualifications, 

 would be out of place here, but the facts which have been given seem 

 to be sufficient to warrant its use as one step in our argument in regard 

 to the relations of the sexes. From this as our basis we will now 

 trace the evolution of sex. 



Among the lowest organisms, animal and vegetable, multiplication 

 is usually by the various forms of asexual generation, budding or 

 fission, or cell-multiplication an organism which has by ordinary 

 growth increased in size beyond the limit of exact harmony with its 

 environment, dividing in this way into two, like each other as well as 

 like their parent. In this way the preservation of the established 

 characteristics of the species' heredity is provided for, but in order 

 that progress should take place, by the preservation of favorable vari- 

 eties, variation must also be provided for. This is accomplished by 

 the process which is known as conjugation : two protoplasmic organ- 

 isms approach, come into contact, and a transfusion or mixture of the 



