HEREDITY 



53 



by spores, gemmae, bulbs and tubers, and the artifically 

 severed buds and scions used in grafting and " slipping." 

 3. In sexual reproduction there intervene between par- 

 ents and offspring, not only the complicated reduction 

 divisions involved in the formation of the gametes, but 

 also the nuclear and cell-fusions accomplished by the union 

 of the egg and sperm in fertilization (Fig. 38), Both proc- 

 esses the formation of the gametes, and their fusion 



FIG. 38. Fertilization in the white pine (Finns Strobus). The smaller 

 sperm-nucleus (above) is imbedded in the (larger) egg-nucleus. The fu- 

 sion of the nucleoplasms will finally become more intimate. (After 

 Professor Margaret C. Ferguson.) 



offer almost unlimited opportunities for alterations of the 

 protoplasm especially that of the nucleus. This method 

 of reproduction, therefore, has the very greatest interest 

 and importance for the study of heredity. In the fertilized 

 egg 1 are united inheritances from two parents from two 

 distinct lines of ancestry protoplasms (germ-plasms) with 

 two entirely different histories extending back into the 



1 The fertilized egg (as Thomson has pointed out) is the inheritance, 

 and becomes, in the mature individual, the inheritor. 



